Abstract: This paper is the study of the gas communication andthe loss of hyd rostatic head of cement column caused by the gelling of cement slurry in the case of simulating the changes of temperature and pressuse in the well bore. From the results of experiments, it has been proved to be true that the gas communication and the loss of hydrostatic head of cement column caused by the gelling of cement slurry are serious, and the loss of hydrostatic head of cement column caused by the gelling of cement slurry can be calculated quantatively after experimentation and mathematical analy-
This makes it possible that a sound basis is provided for taking tech-
nical measures to grevent oil，gas and water co-mmunication in the casingcementiag job.