The invention discloses a series of pyrazolopyrimidinone derivatives, which have the following chemical structure, their preparation methods and use,It has been proved by pharmacological experiment that the said pyrazolopyrimidinone derivatives have high inhibitory activity against PDE5, and parts of them have a much stronger potency against PDE5 than against PDE6. Most of the compounds show low toxicity. The pyrazolopyrimidinone derivatives can be used in clinics for the palliative or curative treatment of symptoms or diseases relating to cardiovascular system, urinary system, especially for the palliative or curative treatment of erectile dysfunction.
