Research on the center of gravity (COG) of the body has wide applications in academic, medical, and other related fields. However, common devices are bulky, expensive, or inconvenient. In addition, most devices detect a two-dimensional center of mass, not a three-dimensional (3D) one. In this research, we proposed a detecting method of 3D COG. Consideration of body balance processes was realized by the rotation of each joint, and the processes could be detected by an inclinometer network installed on each main joint. On the basis of data from this network, we deduced a 3D-coordinate formula for the human COG during a tilted state using an analytical method and coordinate transformation. Then, the 3D coordinates of the COG were obtained by substituting tilt angles into the formula. Twenty subjects participated in the test. Compared with the results from a commercial motion capturing system, the standard deviation (SD) was in the range of 0.10–0.60 cm, which validates the accuracy of the proposed system. The system is convenient, economical, and requires fewer calculations.