Abstract: In order to improve and ensure the accuracy of the measurement data of KI/KIO₃ chemical actinometer, the influences of temperature, time, visible light, solution preparation process, stirring, solution concentration and other factors were studied using the improved aperture-type Collimated Beam Apparatus. According to the chemical reaction of the chemical actinometer, the internal reason of the influence was analyzed theoretically, and the influence of the incident angle was analyzed by geometrical optics. The results show that the blank sample method can effectively eliminate the error caused by the instability of the solution during the whole process. The stability of the solution could be improved by dissolving sodium tetraborate first when preparing solution. The light transmittance of the solution was only 0.56%, and stirring could make the ions diffuse better. The solution's I₃^- had a concentration saturation threshold of 0.001 672 mol·L^-1, indicating that the appropriate UV dose should be selected when measuring. The error elimination method proposed could theoretically eliminate all influences including currently unknown factors.