The invention provides a well-cementing cement slurry volume change testing device, which comprises a kettle body (2), a slurry cup (6), an air source (28), a water source (29), a booster pump (18), a displacement sensor (21), a pressure sensor (25) and a control panel (26) as well as a computer acquisition terminal (27). The invention also provides a testing method using the tester. By adopting the well-cementing cement slurry volume change testing device and method, the downhole temperature and pressure condition can be effectively simulated indoors; the downhole flow state and static state of cement slurry can be effectively simulated indoors; and the small change of the cement slurry volume can be accurately recorded, thus ensuring the accuracy of the testing result.