In 20th century, The development of the world economy and the industry led to the rapid development of national urban transportation, which has also made urban traffic development face enormous pressure, global warming, climate fusion and also gradually rose people's awareness of environmental protection. At this very moment, how to reduce pollution, high energy consumption and high carbon emissions has become an overarching policy of national urban transport development. It has also made the zero-emission carbon and green bicycle traffic develop rapidly. Governments encourage and promote bicycle traffic actively. At this circumstances, this study takes cyclist safety as a viewpoint, discussing the relationship between thechanges of body center's gravity position and the bike's braking performance. Then design and manufacture a safety seat system which can assist the body to move the center of gravity according to the change of bicycle's speed which can surely increase the cyclist's traffic safety and improve the braking performance of the bicycle.