The present invention provides a low-loss high-repetition-rate pulsed laser modulator comprising: a 2*2, 1:1 coupler; a light delay module; a 1*2, 1:1 coupler. The present invention can modulate a low-repetition-rate pulsed laser to be a high-repetition-rate pulsed laser. The basic principle is: one beam of low-repetition-rate pulsed laser can be divided into two beams with the same light intensity by a 1*2, 1:1 coupler; control the two beams of light to have an optical path difference so that when they are coupled into a 2*2, 1:1 coupler, a double pulse repetition rate can be obtained; In the same way, when the two beams of light from former 2*2, 1:1 coupler, with another different optical path difference are coupled into the next 2*2, 1:1 coupler, a double pulse repetition rate can be obtained again; when we obtain the repetition rate we need, a 1*2, 1:1 coupler instead is connected to couple the two beams of light into one beam with a double repetition rate.