Based on Bayesian theory, the compressive strength of existing masonry structure was deduced. Compressive strength tested by the method of axial compression in situ was taken as prior information. At the same time, calculated strength of block and mortar by rebound method was used to construct the likelihood function, according to the GB50003-2011Code for design of masonry structures. And then the posterior distribution of compressive strength was derived. It was shown that reasonable strength combined with various information of compressive strength for existing masonry structures can be obtained. Moreover, the established posterior distribution can be used as the prior information for the next compressive strength reference, and the dynamic long-term observation of the compressive strength for existing masonry structure can be realized. Furthermore the basis for regular maintenance and reinforcement of existing masonry structure can be provided, also the foundation for sustainable development of existing masonry structure can be established.