Abstract: It is typically assumed that the strength of individual particles deteriorates with time when using the discrete element method (DEM) to model the creep behaviour of rockfill materials under loading. Quantifying the time-varying degradation characteristics of actual particle strength is essential for a quantitative analysis. However, effective means to measure these characteristics are currently lacking. To address this issue, a measurement method that integrates experimental testing with theoretical analysis is proposed in this paper. In this method, the creep compliance of individual particles is determined by a uniaxial compression test with a multiple-stage constant loading history. Moreover, theoretical analysis is employed to obtain the spatiotemporal evolution of the strain field in individual particles under a single-stage constant loading history. The calculation equation for the particle failure time is then derived based on the maximum tensile strain theory. Finally, the time-varying degradation process of the particle strength is characterized by a quantitative relationship between the load level and the failure time. Preliminary applications on limestone particles (10 − 50 mm) verify the effectiveness of this method. The results also exhibit that the relationship between the load level and the failure time follows an exponential function. Meanwhile, the decay parameter shows a lognormal distributional randomness, and the randomness of the load level corresponding to the long-term strength obeys a beta distribution. The proposed method provides a viable solution to quantitatively measure the time-varying degradation characteristics of rockfill particle strength.