Abstract: The drugs such as sildenafil adulterated in herbal products and dietary supplements may endanger human health. The number of the new modified derivatives is increasing recently. Based on Q-TOF-MS, a new sildenafil analogue was found. It was isolated and purified by preparative liquid chromatography. Its structure was determined by NMR, as 1-4-propoxy-3-(6, 7-dihydro-1-methyl-7-oxo-3-propyl-1H-pyrazolo4, 3-d pyrimidin-5-yl)phenylsulfonyl-4-methylpiperazine. Compared with sildenafil, the ethoxy group of the benzene ring moiety was moved to the propoxy group, which had not been reported in China. The mass spectrometric behavior pattern of the structure type was summarized, which can greatly accelerate the structural analysis of novel analogues.