It is a crucial approach to convert the new energy that cannot be absorbed into the grid into DC transmission to promote the “West-to-East Transmission Project” and large-scale absorption of new energy. It urgently requires the research of the ultra-high voltage direct current (UHVDC) location planning technology to support the safe and economic operation of the power grid. This paper considers the support capability of the multi-DC external power joint optimization for the transmission power grid. It also establishes a collaborative planning model of the DC location and the transmission grid based on the balance of safety and economy. A grey comprehensive optimization method based on moment estimation theory weighting is proposed to solve the problem. Finally

taking the Ningxia grid as an example

Tiandushan Substation is the optimal sending DC location considering economy and safety

which is consistent with the actual experience and verifies the effectiveness of the method and model proposed in this paper.