Abstract: Aiming to resolve the problem that the down-hole environments(HTHP and restrained)canimnot be simulated by the popularly used methods,and the measurements of laboratory experiment are impractical,a testing device,named measuring instrument for evaluating volume stability of HTHP cement slurry,was developed.The instrument can simulate the down-hole environment and measure the expansion rate of cement slurry continuously when it is in plastic state and hardening state.The process of experiment is recorded and the curves of temperature-time,pressure-time and height increment-time are drawn by data acquisition and management software.There are two measuring sensors which can complete a comparison test and the results are compared with the test detected by spiral micrometer and measuring cylinder.It was shown that data derived from this device was smaller and more reliable than spiral micrometer used to detect the cement slurry with crystalloid expanding agent.Volume stability of the cement slurry with gas former,which can not be evaluated by normal methods,can also be appraised by this instrument.The experiment showed that the device could be used for evaluating volume stability,oil cement additive optimization and formulation designing.However,the graphical interface of data acquisition and management software should be simplified because it was not concise.