The embodiments of the present application disclose a method and device for sending and receiving an optical signal. The method for sending an optical signal comprises: performing serial-to-parallel conversion on a data signal to be transmitted to obtain an I path data sequence, a Q path data sequence and a PPM path data sequence which are in parallel; performing mPQ-encoding on the I path data sequence, the Q path data sequence and the PPM path data sequence to obtain an I path and a Q path of an mPQ-encoded digital signal; shaping the I path and the Q path of the mPQ-encoded digital signal by Nyquist-filtering to obtain an I path and Q path of a filtered digital signal; performing digital-to-analog conversion on the I path and the Q path of the filtered digital signal and mapping the converted I path and Q path onto an optical carrier to obtain a target optical signal and send the same. By applying the embodiments of the present application, spectral efficiency loss in optical communication can be reduced or even eliminated while power efficiency is increased.