Abstract: Aiming at the new energy power supply control characteristics lead to the new energy transmission line fault after the crossing current increases, resulting in the existing current differential protection of the differential current decreases, restraint current increases, the protection sensitivity decreases, increasing the risk of protection refusal. This paper presents a new principle of differential protection utilizing combined current and voltage restraint principle. In the current restraint dimension, the complex plane of current differential protection is established, which breaks away from the constraint of Kirchhoff's current law on the threshold value of current differential protection. Based on the complex plane reflecting the current phase relationship on both sides of the line, the operating characteristics of current restraint principle are constructed to solve the problem of protection maloperation caused by the unbalanced current outside the area. In the voltage restraint dimension, the line conductance characteristic complex plane is established to reduce the dependence of the compensation capacitor current on the line parameters, eliminate the influence of the crossing current on the protection sensitivity during the fault in the zone. Voltage correction technology and high voltage low cosine value blocking technology are proposed to solve the problem of low voltage dead zone and high voltage sensitivity. Finally, a new principle of current differential protection is established based on the combined restraint principle of current and voltage. Simulation results show that the protection principle can still operate reliably when the fault current of the new energy transmission line is only 500 A, doubling the sensitivity compared with the existing protection, and providing high reliability in case of out-of-area faults. Solve the problem that the existing current differential protection sensitivity is seriously insufficient due to the increase of fault ride-through current of new energy transmission line, and create conditions for large-scale new energy consumption.