Through comparson of the numeric difference between diffuse irradiance measured with rotating shadow-band pyranometer (RSP) and standard reference pyranometer, the influence of meteorological elements like global irradiance, ambient temperature, relative humidity and solar spectrum, etc. on measurement errors of diffuse irradiance measured with RSP is analyzed, based on the analysis, a new algorithm of correcting diffuse irradiance measured with RSP is proposed. The algorithm constructs an error modifier prediction model based on support vector regression (SVR) theory first, and then diffuse correction algorithm of RSP can be derived from mentioned prediction model. Applying the correction algorithm to the diffuse irradiance data measured by Solar Radiation Research Laboratory and Lowry Range Solar Station, mean deviaiton and root mean square error of the two stations′ data after correction decrease to -0.2 W/m2, 3.3 W/m2 and 1.9 W/m2, 8.5 W/m2, which indicates that the algorithm is effective and applicative. Meanwhile, compared with Vignola correction algorithm and Vignola and Augustyn (VA) correction algorithm, the algorithm presented can avoid respective undercorrection and overcorrection of similar correction algorithm effectively.