In this paper, based on the optimized formulation of olanzapine (OLN) transdermal patch, the role of sorbitan monooleate (SP) in OLN release and percutaneous absorption processes was probed in vitro and in vivo. Rheological test, DSC, FT-IR and molecular modeling were conducted to elucidate the effect of SP on the release process of OLN from transdermal patch. Additionally, the action of SP on the percutaneous absorption process was probed using tape stripping transdermal experiment, confocal laser scanning microscopy (CLSM), ATR-FTIR and molecular docking. The results showed that the hydrogen bonding interaction between OLN and pressure sensitive adhesive (PSA) was weakened by SP, which resulted in a decrease in the cohesive interaction between polymer chains and an increase in the formation of free volume of PSA, thus, the release of OLN from patch was promoted. Meanwhile, the O—H groups of SP interacted with the polar head groups of the ceramides, which increased the fluidity of the skin lipids, thereby improved the ability of OLN percutaneous absorption. In summary, this study demonstrated that not only the release but also the percutaneous absorption processes were promoted by SP. This study provided comprehensive molecular level understanding on the effect of penetration enhancer on transdermal patch and strategies for rationally selection of chemical enhancer for transdermal drug delivery systems.