Abstract: Mountain-based GPS occultation experiment was performed on the top of Mt.Wuling near Beijing city from Aug.1 to 29,2005 for the purpose of the test of refractivity retrieval technique.During the experiment,the radiosonde observation was taken at Xinglong County,SES the Mt.Wuling about 30 km.The state of arts of the mountain-based GPS occultation sounding at home and abroad are described,the inversion algorithm for mountain-based occultation is also discussed.The refractivity profiles below the mountain height are obtained by using Abel inversion method.The comparisons of the refractivity obtained from different GPS receivers are made.The differences between occultation refractivity and radiosonde data are obtained.Based on these analyses,we find that the interior accuracy of the retrieval results is better than 1%; the average deviation from the radiosonde data is 5.9%,the RMS is 5.6%.