Abstract: The SNR of a communication signal is an important indicator of the signal’s quality. Lots of new emerging communication signal processing algorithms need the support of the SNR imformation, therefore, the SNR estimation is an important research field. The SNR estimation algorithms for conventional digital communicaiton signals(such as MPSK and MQAM ) are sorted according to the differences of signal models and the consistency of the described two sorts of algorithm is analyzed. Subsequently, the research advancements and existing problems for various sorts of algorithms have been analyzed. In the end, the important reseach directions have been proposed to resolve the existing problems .