Abstract: With the increase in the penetration of renewable energy, the power flow changes have become more complex. As the key link of the long-term power and energy balance, the requirements to the transmission expansion planning (TEP) are also gradually being raised. The TEP usually takes the upper and lower limits of the transmission capacities as the constraints, which may lead to the problem that some transmission lines are always in the heavy load operation, increasing the security risks of the power systems. Therefore, the load rate indices need to be paid attention to in the TEP. Considering that adding constraints of the annual statistical indices to the two-staged model may couple all the scenarios so that the actual operation of the system cannot be effectively reflected, this paper designs the linear forms for the line heavy rate constraints and the improved DC power flow constraints, and establishes a bi-level TEP model. The upper-level is for the planning decision problem that is used to formulate a planning scheme, while the lower-level for an operational simulation problem that is used to verify the planning scheme. Compared with the two-staged model, the operation problems in the bi-level model is able to truly reflect the operation of the system under the planning scheme without being affected by the constraints of the planning level. The case studies verify the effectiveness of adding the heavy load rate constraints in the planning and the rationality of the bi-level model structure.