Disclosed are an N-substituted pyrazolo [3,4-d] pyrimidine ketone compound of formula (I), and a preparation process and use thereof as a phosphodiesterase IX (PDEIX) inhibitor: wherein R′ is selected from isopropyl, cyclopentyl, cyclohexyl, isobutyl, and o-chlorophenyl; when R″═CH3, R represents benzyl; and when R″═H, R is selected from 3-methylpyridine, 1-phenylethyl, 1-(4-chlorophenyl)ethyl, D- or L-configured CHCH3CONHR′″, D- or L-configured CH2CONHR′″, D- or L-configured CH2CH2CONHR′″; wherein R1 is selected from hydrogen, chlorine, methoxy, methyl, trifluoromethyl, dimethoxy, methylenedioxy, and dichlorine, and R2 is selected from hydrogen, methoxy, ethoxy, isopropoxy, methyl, dimethoxy, and 2-methyl-4-methoxy, and wherein R′″ is p-methoxyphenyl.