Abstract: To study the output load loss mechanism of the marbles screw loading device, a force transmission model was established emphatically on frictions and unbalanced loads. Based on the structure and motion characteristics of the device, the impact of frictions and unbalanced loads on the device output was analyzed with Coulomb friction law and Hertz contact theory. The force transmission efficiency formula was deduced from the quasi-static equation of the device. Meanwhile, the relevant parameters in formula were discussed. The results show that the friction at the ball groove seriously affects the force transmission performance, the optimum helix angle of the device is 19.88°, and the matching size of the ball groove and the marble can be adjusted to improve the force transmission characteristics of the bullet.