Abstract: Based on the principle of measuring the solar diameter by CCD astrolabe, a method of reducing the data of the solar images is proposed and tested, and 8 frames of the solar images exposed on a CCD chip for each of three seeing conditions areyielded. Based on these frames of exposures, adopting digital image reduction technique, accuracy of measurement of the solar diameter is estimated and analysed. Theresults of simulating observation and computation show that CCD astrolabe couldmeasure the solar diameter with accuracy better than 0.05" for both the scheme ofa single image and the scheme of couble images.