At present, in the case of backpacks for the youth on the market, weight is mainly designed to be carried by shoulders, which ignores the role of the waist in load-carrying. Long-term improper loading of backpacks can affect the growth of one’s spine. In order to balance the load on shoulders, waist, and hip, a weight loss backpack was designed to change the way of gravity transmission through the hip belt and elastic bar structure. Firstly, the biomechanical analysis of the state of the human backpack and the spine was carried out, and the weight-reducing principle of the backpack was achieved according to the force analysis. Then, the torque analysis was carried out on shoulders, waist, and hip of the weight-reducing backpack, and a design plan was proposed. Next, the traditional backpack was analyzed by ADAMS. The dynamic simulation of human shoulders, waist, and hip loads was carried out with the weight-reducing backpack under three road conditions of even ground, uphill, and downhill conditions, and the moments of shoulders, waist, and hip in the cases of the two backpacks were analyzed by MATLAB. The results show that the weight-reducing backpack could reduce the shoulder moment by 6.1% and the waist by 5.4%; the ratio of the shoulder moment of the weight-reducing backpack to the combined moment of the waist and hip was 4.17, and the ratio of the traditional backpack was 6.58. A conclusion could be drawn that the weight-reducing backpack could reduce the load on shoulders and waist. At the same time, it was found that the smaller the ratio of the shoulder moment and the combined moment of the waist and hip is, the greater the moment transferred to the hip, and the better the balance of the backpack, indicating that the weight-reducing backpack outperforms the traditional ones.