A testing device for measuring the curing shrinkage rate of solid propellants was developed in this study. In addition， the online monitoring test of curing shrinkage of HTPB/IPDI propellant was carried out. The relationship between curing shrinkage and time during the curing process of solid propellant was obtained. By constructing the relationship between curing shrinkage， curing degree and curing kinetics， the curing degree change law and curing kinetics model of solid propellant during curing process were obtained. The results show that the curing shrinkage of solid propellants changes in a three-stage S-type. The maximum curing shrinkage is about 0.108%， and the maximum curing reaction rate is 7.809×10^-6. During the isothermal curing process， the curing reaction rate curve of HTPB/IPDI propellant shows a bell-shaped curve， so the thermal curing of solid propellant has autocatalytic characteristics. The pre-exponential factor A₀ of the self-catalytic kinetics model for HTPB/IPDI propellant is 379.087 s^-1. The reaction orders m and n are 0.711 and 1.501. The results provide a new method to test the shrinkage of propellant and clarify the curing reaction characteristics of composite solid propellants.