The invention discloses a mean free error time assessment method and system based on an irradiation test satellite-borne responder. The method includes the following steps that (1) the particle variety of an irradiation test is selected according to orbit space environment of the satellite-borne responder arranged in a satellite; (2) particle beams of selected particles are transmitted, a timer is started, and a remote control function module, a remote measurement function module and a distance measurement function module are monitored in real time; (3) when it is monitored that output information of any of the remote control function module, the remote measurement function module and the distance measurement function module is matched with set error code information, the timer is stopped, and the particle beams are stopped from being transmitted; (4) particle fluence and the function flipping rate are calculated, so that ratio information is obtained; (5) the mean free error time is calculated according to the ratio information and bit flipping rate information of the satellite-borne responder in the corresponding orbit space environment.