A device of light pressure detection was designed. The device based on Mach-Zehnder interference theory, and had modulation and amplification interference optical path. The deformation (displacement) of double reflection aluminum film caused by the laser pulse with different frequency and power. The light generated by HeNe laser was split to the reference light and the signal light by a semi-reflecting and semi-transmitting mirror. The optical path difference of the reference light and the signal light was changed because of the thin film shift. Therefore, it caused the movement of interference fringes. The displacement of interference fringes were recorded by CCD, and then the relationship of fringes movement and the film deformation was calculated. At last, the light pressure was obtained. The effects of pulsed laser incident angle, frequency and other parameters were discussed in detail and the thermal radiation effect is eliminated by using the method of double incidence angle. The device could measure the minimum pressure (13.42 μPa) produced by the minimum optical power of 15.0mW. The linear range is from 15mW（13.42 μPa）to 200（13.42 μPa). The device works steadily, with high sensitivity and accuracy.