The invention aims to provide an insulation support and a mutual inductor and a circuit breaker applying the same. The insulation support is used for solving the problems that an outgoing mode of a secondary coil of the mutual inductor is not reasonable to cause that a bolt with a relatively high level discharges towards an outgoing conductor of the secondary coil with a relatively low level along a surface of the insulation support in a flashover way or breaks down the insulation support, a part of a current transformer is damaged and the current transformer is not stable in working and short in service lifetime.