The invention discloses pyrazolo[3,4-d]pyrimidone compounds and application thereof in preparation of a phosphodiesterase IX inhibitor. The structure of the compounds is shown as a formula (1); in the formula, when R' is 2-chlorophenyl, R refers to phenyl, substituted phenyl, benzyl, substituted benzyl, 3-methylpyridine, 1-phenylethyl, diphenylmethyl or CHCH3CONHR1, wherein R1 refers to phenyl ormethyl, methoxyl, ethoxyl, isopropoxy, methylthio, NHCOCH3 or NCH3CH3 substituted phenyl; when R' is phenyl, R refers to CHCH3CONHR2, wherein R2 refers to methoxyl or ethoxyl substituted phenyl; and when R' is methyl, R refers to 4-methoxy-benzyl, diphenylmethyl or N-(2-amino-cyclohexyl)-4-methoxy-benzenesulfonamide. The pyrazolo[3,4-d]pyrimidone compounds have activity of inhibiting phosphodiesterase IX, can serve as the phosphodiesterase IX inhibitor, can be used for preparing the phosphodiesterase IX inhibitor, and have wide application prospect. The compounds are shown as the formula (1).