experts at top universities and lawyers said political reform had not matched the quick pace of economic expansion.
"If reforms to the system urgently needed by Chinese society keep being frustrated and stagnate without progress then official corruption and dissatisfaction in society will boil up to a crisis point and China will once again miss the opportunity for peaceful reform and slip into the turbulence and chaos of violent revolution " they wrote.
The letter began being circulated on the Internet earlier in December but online references to it in Chinese media reports have now been removed.
The government, which since 1949 has been controlled by the Communist Party, needed to push democracy and independence of the judiciary as well as deepen market reforms, the letter said.
He Weifang, a law professor at Peking University and one of the signatories told Reuters, he believed the demands were rather moderate but that now was the time to make them as President Hu Jintao prepared to hand over the reins of state power to Xi Jinping who was made party chief in November.
"We have come to that period again when the leadership is changing. People expect continuing advances when it comes to reform of the political system " he said.
"The Chinese people including intellectuals have been talking about this for a while but little has happened. So I think we have the opportunity now to push it again."
Other signatories include Zhang Sizhi, defence lawyer for Mao Zedong's widow, Jiang Qing, leader of the "Gang of Four" that wielded supreme power during the 1966-76 Cultural Revolution.
She was given a suspended death sentence in 1981 for the deaths of tens of thousands during that period of chaos.
About 65 Chinese academics, lawyers and human rights activists have signed a similar letter demanding top party members reveal their financial assets, saying it is the most fundamental way to end corruption.
Analysts have been searching for signs that China's new leaders might steer a path of political reform, whether by allowing freer expression on the Internet, greater experimentation with grassroots democracy or releasing jailed dissidents.
But the party which brooks no dissent to its rule and values stability above all else has so far shown little sign of wanting to go down this path despite Xi trying to project a softer and more open image than his predecessor.
However, Xi himself warned shortly after becoming party boss that if corruption were allowed to run wild, the party risked major unrest and the collapse of its rule.
The letter said democracy, rule of law and respect of human rights were "a global trend that could not be stopped".
"China s 100 years of bloody and violent history -especially the painful and tragic lesson of the decade-long Cultural Revolution - show that once we go against the tide of democracy human rights rule of law and constitutional government the people will suffer disaster and social and political stability will be impossible", the letter said.