Research conclusions: Through studying of two estimating method, it is fixed that capacitor per km of Qinghai-Tibet railway continuous power cable lines is between 0. 124 0～0. 133 1 uF, Then three compensation modes, namely, undercompensation, overcompensation and synthesized compensation are discussed through simulating and calculating to confirm whether it can satisfy the operating demands in all kinds of power transmission. A decision to adopt undercompensation was made to avoid resonance and lead to more fault. When overhead lines and cable lines run together, it has a little impact to the cable when overhead lines cast in, on the contrary, it has much more impact to the overhead lines when cable lines cast in, but it would be sustainable. After analyzed the over voltage，the conclusion of it would satisfy the system operational reliability and overvoltage needs if it adopted the undercompensation, both cable line end grounding method and reactor neutrality point grounding method. When one phase has a grounded fault, the other two phase voltage would turn into line voltage，just like the usual little current grounding system.