In a spiral galaxy, the stars move in a circular motion around the galactic center, and the relation between velocity and the orbital radius is referred to as the rotation curve. Previous astronomical observation data indicate that the rotation curve is flat at the periphery of the galaxy, which completely dissatisfies Keplerian decline. Assuming that the galaxy is surrounded by a dark matter halo, the additional gravity of the dark matter halo can explain flat rotation curves well. The rotation curves can be roughly simplified into two parts. The velocity is directly proportional to the orbital radius inside the galaxy and remains almost unchanged at the periphery of the galaxy. By comparing a star's circular motion with the circular motion of a silicone ball on the curved surface, the gravitational potential well of a spiral galaxy was calculated and plotted in this study. Using a 3D printer, the gravitational potential well was printed. A small silicone ball was forced to undergo circular motion in the printed gravitational well to simulate the motion of the star in the spiral galaxy. Using this interesting method, students in astronomy and physics can develop potential well of the spiral galaxy by themselves, so as to deepen their understanding of rotation curves of galaxies.