The tilt between CCD and diffusion screen will result in the spot geometry and intensity distortion,which will worsen the measurement result of spot distribution. The reason for distortion is analyzed,and the position relation between distorted grids and ideal grids is established by polynomial model. A grid method of rectifying distortion based on uniting pixels is presented. The distorted image of the self-designed and fabricated “standard grid target board” corresponds the standard grid through distinguishing from the borders of the grids. The corresponding relation can help to recover the spot geometry. It can rectify intensity distortion through the image of uniform light. Experiments prove that the means can not only calibrate the spot geometry but also rectify intensity distortion. The calibrating precision is within 1%. The method is very practical in measuring laser intensity distribution.