Disclosed is a 2-morpholin-4, 6-disubstituted pyrimidine derivative as shown in formula (1) below, and a pharmaceutically acceptable salt, solvate, stereoisomer or prodrug thereof, and a pharmaceutical composition thereof and a use thereof, wherein the definition of each group is as shown in the description. The compound has a PI3K kinase inhibition activity, and has a relatively high inhibitive ability and a low cytotoxicity against PIK3CA mutant breast cancer cell strains T47D and MCF-7.