Considering that the space for line installation is not enough,DC transmission projects for mid-and short-distance (800~1 300 km) in China recently are designed to be contrusted by±500 kV double circuits on the same tower,and the transmission capacity of single circuit is rasied from 3 000 MW to 3 200 MW,which lead to the increased loss,and more difficulty in the converter valve design etc.Aiming at the DC transmission project from Xiluodu to Guangdong,the feasiblity of the voltage raised from ±500 kV to ±535 kV or ±550 kV is studied,and the effects of three voltages are analyized on main circuit parameters,insulation coordination,main equipments,DC line design,loss and investment.As a result,the optimized operating voltage is given by a comprehensively technological and economic comparison.