Abstract: The mechanical property of cementing set cement has a direct influence on the long-term sealing effect of cement sheath. The mechanical property parameters of cementing set cement are measured mainly by means of triaxial mechanical test, and effective sample preparation is crucial to triaxial mechanical test study of cementing set cement and the integrity analysis of cement sheath. Considering the peculiarity of the samples for the triaxial mechanical test of cementing set cement, two sample preparation methods were designed and explored. One is prepared from the coring cube after the curing and shaping of cubic set cement, and the other is prepared through primary curing and shaping in a mould. Then, two sets of cylindrical set cement curing moulds used for mould curing based sample preparation method were developed, i.e., small sample Ø25.4 mm×50.8 mm and large sample Ø50.8 mm×101.6 mm. Finally, 56 sets of mechanical test data of the samples prepared using different methods were comparatively analyzed by virtue of scatter distribution, root-mean-square error (RMSE) analysis and standard deviation analysis. It is indicated that small sample mould based sample preparation and curing method is superior to the other methods in terms of data reliability, sample preparation efficiency and cost, so it is recommended to act as the sample preparation method for the triaxial mechanical test of cementing set cement.