In this paper, we present an early stopping criterion for low density parity check (LDPC) codes decoding based on Chinese Mobile Multimedia Broadcasting standard (CMMB) while preserving a good performance. To reduce the average number of decoding iterations, it is crucial to detect undecodable blocks at the beginning of the decoding process. The proposed stopping criterion for undecodable blocks is based on the estimation of the variable node reliability (VNR) and this stopping criterion has to be switched off when VNR passes a threshold. Simulation results show that the proposed approach can effectively reduce the average number of iterations at low SNR region where most blocks are undecodable, meanwhile the performance loss at all SNR region is negligible.