A compound of formula (I) and citrate thereof as inhibitors of type 5 phosphodiesterase (PDE5), their preparation methods, and a pharmaceutical composition comprising the compound of formula (I) and citrate thereof are disclosed in the present invention. The trial of the present invention proves that the compound of formula (I) and citrate thereof can inhibit the activity of PDE5 and can be used for treating erectile dysfunction, inhibiting platelet aggregation and treating thrombosis, decreasing pulmonary artery hypertension and treating cardiovascular diseases, treating asthma and treating diabetic gastroparesis.
