The invention provides a 1-[3-(6,7-dihydro-1-methyl-7-oxo-3-propyl-1H-pyrazolo[4,3-d] pyridine-5-group)-4-ethoxy-benzenesulfonyl]-cis-3,5-dimethylpiperazine citrate or an Aildenafil citrate crystal form O and a preparation method thereof. And the invention also provides pharmaceutical compositions containing the Aildenafil citrate crystal form O and the use thereof in preparing drugs for treating Male Erectile Dysfunction (ED). The above crystal form O can be prepared through the steps of: dissolving a raw material, namely, the Aildenafil citrate in a mixture of distilled water and tetrahydrofuran, stirring, heating, filtering, stirring a filtrate, cooling, insulating heat, crystallizing, filtering and the like. The crystal form O can be adopted to prepare drugs with pharmaceutically acceptable excipients, so as to treat the male sexual dysfunction diseases.
