A device capable of quickly and accurately adjusting output signal light interference of two optical cavities comprises a laser device, the first optical cavity, the second optical cavity, a first beam splitting unit and a second beam splitting unit and also comprises an auxiliary light unit which intercepts and captures first base frequency light output by the second beam splitting unit, uses thefirst base frequency light as auxiliary light to be output to the first base frequency light and then injects the light into the first optical cavity and the second optical cavity along reverse lightpaths of first base frequency light and second base frequency light after beam splitting. By converting the interference of output signal light of the two optical cavities uneasy to adjust into adjustment of mode matching between one beam of auxiliary light and the two optical cavities, the interference adjustment process is simple, quick and efficient, and the accuracy is high, an auxiliary light source is directly guided from an existing light path without introduction of a new light source element, the auxiliary light coincides with an original light path, and the device is simple in structure and low in cost. The output signal light in the two optical cavities are reshaped into parallel light by utilizing one auxiliary light path, so that signal light is more convenient to transmit and reshape in space.