The invention belongs to the technical field of medicines and specifically relates to a phosphodiesterase-5 inhibitor as shown in a general formula (I) and a pharmaceutically acceptable salt or a stereoisomer thereof, wherein R<1>, R<2>, R<3>, R<4>, R<5>, L and W are as defined in the description. The invention further relates to preparation methods of compounds, pharmaceutical compositions containing the compounds, and applications of the compounds and the pharmaceutical compositions in preparation of medicaments for treating and/or preventing diseases related to sexual dysfunction and lower urinary tract symptoms.