An analytical study on transmitted intensity perturbance of air-gaped Glan-type polarizing prisms with varying rotation angle is given. The perturbance strongly affects the quality of transmitted polarizing light. Our study shows that the t ransmitted intensity sensitively relies on the incident angle. The minute random variation of the incident angle around the structure angle of air-gaped Glan-ty pe polarizing prism gives rise to the perturbance found in the experiment. The i nfluence of the variation of temperature on the disturbance is discussed. Effect ive ways for reducing the disturbance are presented.