With the increase of service life, the concrete strength of existing RC building structure degradates. To study the change law of the time-dependent compressive strength of concrete under freeze-thaw environment, the compressive strength of concrete of existing RC buildings in Harbin, Jilin and its surrounding areas was tested on the spot by combining ultrasonic-rebound stress test with core-drilling method. By normalizing and merging 924 groups of concrete compressive strength data, nonparametric test method was adopted to determine the probability distribution function of the normalized concrete strength, and the relationship between relevant parameters and service age was analyzed by regression analysis. The test results show that under freeze-thaw environment, the modified time-varying model of ultrasonic-rebound stress test satisfies the linear variation law, the time-dependent concrete compressive strength obeys normal distribution, the variation of mean value and standard deviation of concrete relative compressive strength with service age can be fitted by quadratic polynomial model and linear model respectively.