The planar force model of prepreg, initially established based on the principle of minimum potential energy and the Rayleigh-Ritz method, was improved by considering the difference between the tensile and compressive moduli in the direction of the prepreg fibers. Compressive-tensile stress distribution coefficients were also established. Combined with tests on the effect of process parameters on interlayer tack, a theoretical prediction model for the turning radius related to process parameters was developed, and the impact of prepreg interlayer tack force on the minimum turning radius was analyzed. A finite element simulation model for prepreg curve placement was created to study the size and distribution patterns of folds generated during the prepreg turning process. A minimum turning radius test was conducted to establish evaluation criteria for surface defects in curve placement and verify the accuracy of the minimum turning radius prediction model. Based on this, a prediction method for the minimum turning radius of prepreg related to process parameters was established, providing constraints for the trajectory design of variable-stiffness placement composites.