The invention provides a photoisolator. A first polarization beam splitting device, an optical rotation device and a second polarization beam splitting device are arranged on the photoisolator along a light path direction; a first diaphragm is arranged between the first polarization beam splitting device and the second polarization beam splitting device on the photoisolator; the first diaphragm comprises a first barrier part which is arranged between a first beam splitting optical path and a second beam splitting optical path of the first polarization beam splitting device; a barrier part of the diaphragm is arranged between the first beam splitting optical path and the second beam splitting optical path; and return light with a certain angle is blocked through the barrier part. Through ingenious arrangement of the barrier part, the return light with a variable angle is effectively blocked under the condition of not influencing normal use, and thus the optical isolation performance of the photoisolator is effectively improved.