I'd like to add something to the answer provided by pohnpei397 that I think is very important in discussion Sun Yat Sen's influence on modern China; The Three Principals of the People.
This is a political philosophy that Sun created as a plan for making China a powerful nation. It is claimed as a basis for the political ideologies of Mao Zedong, and therefore the underlying political philosphy for all of the People's Republic of China today, although it is more apparent in Taiwan today.
The Three Principals stresses the importance of three things
1) Minzu, which refers to nationalism. In order for China to become great, all of the different ethic groups in China needed to be united to push away imperialist nations. Sun believed that China needed to develope a "civic nationalism" rather than an ethnic nationalism to unite people of different cultures (Muslims, Mongols, Tibetians, etc)
2) Minquan or democracy. Sun believed that the power of the government must come from the people. Now although China is communist, the communist party stresses that in Chinese society it is the people whom give China its power. Sun meant democratically elected leaders, but eventually the communist party takes over and changes the meaning of this principal.
3) Minsheng or welfare. This refers to Sun's belief that the ideal Chinese government can provide its people with food, clothing, housing and transportation. These are areas of focus echoed by the government of China today.
Include this in your assignment and your teacher will think you're a rockstar! If you need more help, message me! Good luck.