Aiming at Fused Deposition Modeling (FDM) gradient color printing, a method to predict and evaluate gradient effects is proposed. Using the MFC application development platform provided by Visual C++ program software, two gradient colors were simulated. By changing the amount of color subdivision in the software to obtain the images of different gradient effects, the prediction of gradient effects was achieved. In order to achieve colorful printing, a colorful printer was designed. Firstly, the gradient color printing experiment was performed. The gradient effects of the parts printed under the color subdivision amount corresponding to the simulation and simulation results were analyzed by software. The correctness of the simulation results was verified and the gradient effects were evaluated. Then the multicolor printing experiment is carried out to realize the colorful 3D printing. Moreover, it provides reference for the further study of colorful 3D printing technology.