The invention discloses a method for adjusting step length based on joint simulation of a power system and a communication system. The method comprises the following steps of judging if data to be transmitted exists in the current step length or not; if the data to be transmitted exists in the current step length, judging if the communication error or the outputted data error of the power system simulation system exists or not; if the communication error or the outputted data error of the power system simulation system exists, reducing the current step length according to a preset step length reduction strategy; if the communication error or the outputted data error of the power system simulation system does not exist, increasing the current step length according to a preset step length increasing strategy; judging if command information to be sent exists in the adjusted step length exists or not; and if the command information to be sent exists in the adjusted step length, updating the adjusted step length into a smaller step length. The invention also provides a device for adjusting the step length. The problem of step length adjusting in the simulation of two systems is solved.