Abstract: Ionosphere delay error is an unneglectable error source in the propagation of radio signal. The GPS authorized users utilize dual-frequency observations of dual-frequency receivers to determine the ionosphere delay in real time, so the measured results have a high precision. Compared to authorized users, most general users use the ionosphere model to correct the delay error when they utilize single-frequency receivers. Relative to dual-frequency observations, the correction effect by ionosphere model is not ideal. In this paper, dual-frequency observations are used to verify the Klobuchar model which chosen by GPS broadcast ephemeris has a widespread application in single-frequency receivers. Ten days' data of WUHN Observation Station has been picked up to analyze Klobuchar model, and the obtained results were consistent with previous researching results. Also, a new improvement method is proposed based on previous analysis. Since the variability of ionosphere has a close relationship with the Sun's activity intensity, and the sunspot relative number is a symbol reflecting the Sun's activity intensity, the new improvement method is realized by means of sunspot relative number to modify Klobuchar model. This improved method has been proved with a large scale promotion in the correction effect through experimental data. Relative to original model, the correction rate greater than 50% has upgraded from about 60% to 85% above, and that greater than 80% upgraded from 10% to 40% above. In practical application, users of single-frequency receivers can refer to this improvement method to correct Klobuchar model.