Abstract: In order to study the error propagation process of the GNSS radio occultation , the impact of random errors of excess phase delay on retrieved bending angle were deduced theoretically during the retrieval process of excess phase delay to bending angle in this work. For GPS and LEO satellites, under the condition of precise orbit determination, neglecting the impact of orbit error to the retrieval results, treat orbit parameters as constant, consider the impact of random errors of excess phase delay on retrieved bending angle ?s errors . In this research, EGOPS simulation software were employed to simulate the data of atmospheric excess phase delay. CHAMP real orbit data, MSIS-90 atmospheric model and full 3D ray tracing program were using in the Forward Model, and one occultation event was selected to validate the error propagation model. The research results show that the changes of excess phase delay can bring corresponding bending angle errors. Random errors of 5cm, 1cm and 1mm are added on the excess phase delay and then the bending angles are retrieved, it is found that the corresponding bending angle errors are less than , and respectively.For the purpose of statistical analysis, 20 occultation events were selected randomly, and the bending angles mean bias were given that induced by excess phase which 1cm random error were added. The results are slightly larger than the error characteristics of case studies, but entirely consistent with the model,the retrieval bending angle errors are within .Through the statistical analysis processing, the model we have derived are validated.