Abstract: Ultraviolet (UV) curing technology has the problem of limited curable thickness. However, the in-situ photocuring process has a unique advantage in curing large thickness composite materials by stacking and curing layer by layer. In order to achieve the goal of simultaneous curing and uniform curing degree of each layer in the in-situ photocuring process, the mathematical model of single layer UV curing was presented. Based on this model, a mathematical model was established, which could describe the entire in-situ photocuring process. The time to add each layer was then optimized, the optimal layering time was solved by genetic algorithm combined with gradient descent algorithm. In addition, the in-situ photocuring process was simulated by finite element method. The simulation results show that compare with other curing methods, after optimizing the layering time of in-situ photocuring process, each layer will complete curing when the curing end time is reaching, and the curing degree is uniformly distributed within the median of the desired curing degree. The algorithm and simulation are verified by curing experiment of glass fiber reinforced resin matrix composite laminates. The comparison between experimental results and simulation results shows that the optimized in-situ photocuring process can achieve the goal of simultaneous curing.