The invention provides a fiber coupling method for a high-power laser test system. A high-power parallel laser beam to be tested passes through an attenuator, a first lens, a second lens and a fiber receiving end face in sequence and then enters a fiber; the first and second lenses form a telescopic beam reducing system, and the surface of the first lens is imaged on the fiber receiving end face through the second lens; and the fiber receiving end face is positioned on an optical axis of the telescopic beam reducing system consisting of the first and second lenses and is vertical to the optical axis. The fiber coupling method of the invention stably couples the laser beams with large directional drift and large transverse deviation into a fiber by the combination of the optical telescopicbeam reducing system and an optical imaging system. The fiber coupling method of the invention is simple, feasible and easy to operate and is particularly applied in the test of the time waveform of a high-power laser pulse.