Abstract: Polar braided composite rotors have received extensive attention due to their lightweight and high radial strength. However, due to their complex fiber structure, further research on mechanical properties is urgently needed. In this paper, based on the meso-structure characteristics of the polar braided composite rotor, a variable unit model was constructed, and three representative volume elements (RVE) based on the yarn structure were described. The elastic parameters of the variable unit model were calculated. The accuracy and effectiveness of the variable unit model were verified by tensile experiments. In order to further explore the mechanical behavior of the polar braided composite rotor under rotating load, a finite element model of the rotating deformation of the composite rotor was established, and the stress and deformation characteristics of the variable unit model and the homogenization model under three different braiding parameters were compared and analyzed. The results show that the different braiding parameters cause the change of the stress concentration position of the rotor. Compared with the homogeneous model, the variable unit model describes the yarn structure characteristics of the rotor. The yarn structure causes the stiffness difference between different units and the stress concentration phenomenon. With the change of braiding parameters, the average difference of radial stress on both sides of RVE-c in local position is 22.4 MPa, 37.8 MPa and 63.9 MPa, respectively, and the difference of hoop stress is 6.5 MPa, 10.6 MPa and 16.5 MPa, respectively. The increase of the density of the circumferential yarn and the radial yarn reduces the stress level of the inner hole and the outer edge of the rotor respectively. The difference of rotor stress distribution is caused by the yarn position, and the difference of stress distribution curve is more significant with the change of yarn arrangement density.