Micro displacement measuring device with high precision based on the principle of grating interference has high voltage sensitivity, thus weak jitter can cause irreparable impact on measuring results. These jitters include the air jitter, the ground vibration, and the fluctuation of the light source, etc. It becomes crucial for how to restrain the influence of outside jitter on the measurements of micro displacement effectively. Firstly, a series of experiments and analyses was carried on for the power fluctuation of the linearly polarized He-Ne laser, which drew that the power fluctuation range of light was greater than 7% which exceeded the fluctuation limit of 1%. Then, using the compensation measures of two signal acquisition and scaling operation, anti light disturbance came true. The analysis of experimental data shows that the effect of light source fluctuation on output voltage can be suppressed effectively through the compensation of optical path and scaling operation. The final amplitude of fluctuation of the output voltage is reduced by 60% than the initial state, and the displacement measurement error reduced from 1.95×10-7 m to 1.40×10-8 m.