This paper examines the path of new energy development in China against the backdrop of carbon maximum and carbon neutralization, and studies the risk of large scale new energy power transmission. In order to solve the complex uncertainty challenges of renewables power and power grid expansion planning, this paper studies and proposes an optimal economic planning model, which includes the thermal power generation start-up and shutdown expenses during the operation, the hydro power generation expenses of surplus water of reservoir, and the curtail penalty cost of new energy output power, the investment of new planning lines. The model has also considered the constraints of balance for power generation and load consumption, the power change rate, and operation, which are calculated based on the time-series operation simulation of new energy power system. Based on the functions, the process of power grid planning technology has been proposed. The planning model proposed in this paper can consider the new energy power characteristics of generation, realize the optimal planning of different power grid schemes. According to the case study findings, the new transmission line can relieve the pressure of local new energy transmission, while also improving power flow distribution as well as the rate of new energy utilization.