Abstract: Under the background of "carbon peaking and carbon neutrality", new opportunities occur on the energy transition and green development. It is of great significance for the scientific "carbon reduction" to rationally formulate plans for incorporating new energy into the power balance and to guide the planning of thermal power installations. To this end, this paper, taking the Northwest Power Grid as an example, proposes a method to improve the credible capacity of the power balance with new energy considering the cross-regional DC backup peak shaving. Firstly, combined with the output characteristics of new energy, this paper analyzes the change laws of the new energy credible capacities in different spaces and times, and the feasibility to reduce the guarantee rates and improve the new energy credible capacity is put forward. Secondly, by analyzing the mechanism of new energy participating in power grid balance, the quantitative relationship between the increase of new energy credible capacity and the DC cross-region peak shaving is deduced under the condition of reducing the installed capacity of the thermal power. Finally, through illustrating the "peak shifting effects" of the load of the northwest and the east China power grids, the plan for the participation of the sending end power grid in the power balance in the cross-regional DC backup peak shaving is figured our. The example shows that the DC participation in the cross-regional peak shaving may significantly increase the credible capacity of new energy and effectively reduce the start-up times of the thermal power, and augment the power generation of new energy. With the low-frequency and short-term support of DC, the optimal allocation of the UHV cross-regional DC resources may be further utilized, which will improve the clean proportion of the sending end power grid. The scheme proposed in this paper, taking into account the reliability of power supply of the power grid and the demand for new energy consumption, is able to guide the planning of the thermal power and new energy installations, strengthen the top-level design of the scientific "carbon reduction", and serve the goal of "carbon peaking and neutrality".