In order to prolong continuous working time of one transmission line inspection robot, a power supply system with induction charging unit for this inspection robot is introduced in this paper. Special current transformer by which the robot could get power from power line is designed according to the magnetic field condition around the transmission line. Besides, charging circuit for Li-battery pack is also introduced. A fly-back circuit is applied in the circuit to provide precisely accessible input power for charging battery packs. Experimental results show that the power supply system could have good performance on extending the continuous working period of the transmission line inspection robot.