BEIJING  The sentencing of an outspoken literary editor to five years in prison for subversion showed that the Chinese government will not relent in its ongoing crackdown against critics and dissidents, supporters of the editor said Tuesday.

The editor, Tan Zuoren, was sentenced Tuesday morning by a court in Chengdu, the capital of Sichuan Province, for criticizing the Chinese Communist Party by writing and protesting recently against the Tiananmen Square massacre of 1989, when soldiers killed hundreds and perhaps thousands of civilians.

But Mr. Tan’s supporters said he had another black mark against him  he was assembling an independent report on the thousands of children killed when schools collapsed across Sichuan and nearby provinces during a devastating earthquake in May 2008.

Mr. Tan’s lawyer, Pu Zhiqiang, and Ai Weiwei, a prominent artist and friend of Mr. Tan, said in interviews that the government wanted to silence Mr. Tan because of his earthquake work. The central government has tried to stifle any discussion of shoddy school construction, which could expose connections between corrupt government officials and business executives.