When Thoreau went into town to have a pair of shoes repaired, he was arrested for refusing to pay a poll tax meant to support America's war in Mexico. He spent a night in jail. His most famous essay, Civil Disobedience (published 1849), which in its call for passive resistance to unjust laws was to inspire Gandhi and Martin Luther King, Jr., was a result of this experience. The journal he kept at Walden became the source of his most famous book, Walden, Or Life in the Woods (1854), in which he set forth his ideas on how an individual should best live to be attuned to his own nature as well as to nature itself.
Thoreau was a man full of dreams and ideals, writing about nature and philosophy of life. He spoke out on many social issues such as peace, living simply, abolishing slavery, and was a vigorous advocate of civil liberties. He had great influence on American literature and later writers, especially those who focused on nature writing.
3. Five aspects of Thoreau’s nature views
(1)Strong Love for nature
Henry Thoreau liked to walk in the wild; all nature was very attractive to him. Nearly every day, all year round, he was walking outside, exploring and observing every corner in Walden Woods, and the other areas of Concord, and recording in his journals vividly what he heard and smelled and saw. Besides, Thoreau had great passion to explore deeper meanings in nature. "The hen-hawk (red-tailed hawk) and the pine are friends," he wrote,  "what we call wildness is a civilization other than our own." In his famous book, Walden, about the ties between people and nature, he says, "Our village life would stagnate if it were not for the unexplored forests and meadows which surround it." 
     
(2) Pursuit of wild nature
"In Wildness is the preservation of the World,"  he wrote, and with such statements he helped shape the thinking of modern day environmentalists. Thoreau wants wild nature, one untouched by human hands. Thoreau represents this wild vision of nature through various lenses – first, from a naturalist's perspective for the differences between species, and for the changes in distinctive habitats as they evolve over the seasons. Second, he represents it from a historian’s perspective, capturing the way that humans have changed the landscape. This includes his own attempts at farming, which is in tension with his respect for native plants. In the end, the nature Thoreau describes is only about a mile away from the center of town, and not in certain far-off wilderness. But Thoreau wants to remind us that nature is all around us, and there to inspire us to be better than we are.   
(3)Conservation of natural environment
Watching Concord losing its forests and seeing the village expanding into the countryside, Thoreau offered his suggestions. "Each town should have a park, or rather a primitive forest, of 500 or a thousand acres, where a stick should never be cut for fuel, a common possession forever, for instruction and recreation,"  he wrote.
(4)God in nature
Thoreau himself had something perhaps more revealing to tell us about himself and his work. "My profession is always to be on the alert to find God in Nature, to know his lurking-places, to attend all the oratorios, the operas, of nature."  In a river, he found the flow of eternity; climbing a mountain he felt his spirit move closer to God. "I believe in the forest, and in the meadow, and in the night in which the corn grows."  It was as though he could see through Nature to a glimpse of the divine. What might sound to us like a contradiction made perfect sense to him: "Heaven is under our feet as well as over our heads."  Exalting his own small world of Walden Pond and Walden Woods and the Concord countryside, Henry Thoreau exalted nature for all of us everywhere.
(5)Man and modernization 梭罗的自然观对中国生态的反思Thoreau’s Views on Nature(6):http://www.youerw.com/yingyu/lunwen_932.html