A new formula to estimate rock specimen damage parameter and its strain is established by means of ultrasonic velocity test under uniaxial compression. According to the formula ultrasonic velocity characterization with different homogeneity indices under uniaxial compression is analyzed. As the homogeneity index increases

the ultrasonic velocity decline rate increases. This conclusion coincides with numerical test of rock acoustic emission(AE). Regression analysis between rock ultrasonic velocity and strain is carried out based on the test results of rock under uniaxial compression. From the above point of view

the regression equation between rock ultrasonic velocity and strain which is of comparatively high accuracy

is obtained. And it reveals that the established formula is reliable. Kaiser effect of AE will appears when ultrasonic velocity declines obviously according to the discussion of the relationship between ultrasonic velocity and AE during the deformation of rock under uniaxial compression. So the result is helpful to research in-situ stress measurement using Kaiser effect of AE under uniaxial compression.