The invention provides a method and system for testing trigger time-delay of a relay protection tester. The method includes the following steps: triggering a message generating device to send a trigger signal to a splitter, wherein the trigger signal is an optical signal; sending the trigger signal to a message record analyzer and a tested relay protection tester through the splitter; sending a preset message to the message record analyzer according to the trigger signal through the relay protection tester; and outputting a trigger time-delay error of the relay protection tester according to the trigger message and the preset message through the message record analyzer. As the method and system for testing trigger time-delay of a relay protection tester can establish a test scheme without dependence on the absolute time, the homology of the trigger signal is guaranteed; the influence of the time tick error on the test result is eliminated; and the test errors of the intermediate links, such as data transmission and data storage links, can be reduced.