How did sun yat-sen support democracy in china?

sun Yat-sen influenced China by helping to cause the overthrow of the Ch'ing (also known as Manchu) Dynasty.  By doing so, Sun ushered in an era in which various factions fought for control of China.  This eventually led to the victory of the communists.  Sun is revered by both the People's Republic of China (mainland China) and the Republic of China (Taiwan) as the main force in creating modern China.

Before Sun, China was ruled by the Manchus whose hold on power was weakening; China was helpless against Western countries that forced concessions from it.  It was also unable to stand up against Japan in the Sino-Japanese War of 1894.  These things helped convince Sun and others that revolution was needed to fix China's problems.

In 1911, Sun's revolution overthrew the Ch'ing and China entered a new era.  This is the main influence Sun had on China.