In order to improve the adaptability of ring laser gyro (RLG) in the outer space environment, a method about RLG output system based on Fresnel lens is proposed. After being converged by the Fresnel lens, the RLG′ s clockwise and anticlockwise beams forge a new array of fringe patterns in front of the focal plane, where the number of patterns does not change, but the size is significantly reduced. Compared with the ordinary convex lens, the Fresnel lens based RLG readout system may bring up advantages in the spherical aberration calibration and installing convenience. It is validated that compared with the traditional RLG readout system, this system can decrease the size of the beam spot down to less than 1% , enabling a smaller photodiode to be selected, and the radiation damage is significantly reduced, therefore the RLG′s adaptability of RLG in the outer space environment is improved.