Based on the theoretical analyses that power frequency overvoltage generated by long-distance transmission line can be restrained by magnetic controllable reactor(MCR) effectively, the restraint of power frequency overvoltage by MCR is simulated in three different working conditions, that is, no-load line capacitance effect, asymmetric earthing and sudden load shedding. It is shown that parallel MCR is effective to restraining the overvoltage, of which the installation in the tail end of line is better than in the head end and in two ends.