The invention provides an inhibitor for targeted tumor cell surface PD-L1 molecules and an application thereof. The invention utilizes an Odyssey On/In Cell Western Blot screening system to find thatcompounds Cobimetinib (GDC-0973, RG7420), AT7519, Lapatinib, LY2090314 and KU-60019 are capable of showing an effect of excellently restraining PD-L1 expression in different cell experiments under a low cytotoxicity condition, and the inhibiting effect has been verified in two different types of tumor cells. Thus, these compounds (especially KU-60019) are expected to be developed into small-molecule inhibitors for clinically inhibiting PD-L1 expression. Besides, a corresponding kinase thereof also becomes a pharmacological target for researching PD-1/PD-L1 signal channels.