Disclosed is a gap adjusting method which easily adjusts a gap between a bimetal and a crossbar by using a gap adjusting block and an adjusting screw in a trip mechanism of a molded case circuit breaker without a separate additional device. The gap adjusting method in the trip mechanism of the molded case circuit breaker includes setting a reference gap between a crossbar and a bimetal, measuring a total resistance of the trip mechanism and a trip stroke of a switching mechanism to set a compensation gap, placing a gap adjusting block on a position separated from a crossbar by a gap based on the sum of the reference gap and the compensation gap, rotating an adjusting screw assembled with the bimetal to contact the adjusting screw with the gap adjusting block, and adhering the adjusting screw to the bimetal.