The invention provides a bypass fast protection circuit used for a DC circuit breaker. The bypass fast protection circuit comprises a fast protection circuit and a thyristor. The fast protection circuit is connected in parallel with a voltage-equalizing circuit of a DC circuit breaker sub-module, and is used for triggering the thyristor when transfer of a current of the DC circuit breaker from a main branch circuit thereof to a transfer branch circuit fails, and breaking down a high-voltage breakdown diode in the fast protection circuit when the DC circuit breaker sub-module is overvoltage during the current breaking process of the DC circuit breaker; and the thyristor is connected in parallel with the voltage-equalizing circuit of the DC circuit breaker sub-module, and is used for protecting the DC circuit breaker sub-module and transferring the current when transfer of the current of the DC circuit breaker from the main branch circuit thereof to the transfer branch circuit fails. The bypass fast protection circuit can effectively prevent the sub-module from being broken down by high voltage during the breaking process of the DC circuit breaker; and the bypass fast protection circuit is mature, simple and easy to implement, and can effectively improve the reliability and availability of the DC circuit breaker.