The present invention relates to the field of pharmaceutical chemistry. In particular, the present invention relates to a pyridopyrimidine or pyrimidopyrimidine compound as represented by general formula (I), or an isomer thereof or a pharmaceutically acceptable salt, ester, prodrug or solvate thereof, a preparation method, a pharmaceutical composition and uses thereof in preparing an mTOR inhibitor. As the mTOR inhibitor, the compound or the pharmaceutical composition thereof can be used for treating the diseases or symptoms due to PI3K-AKT-mTOR signal path malfunction.