WS2/TiO2 composite layer was successfully in situ prepared by plasma electrolytic oxidation method adding Na2S and Na2WO4 into electrolyte. The structure, morphology and frictional properties of the composite layer were investigated by X-ray diffraction, scanning electron microscopy, and 3D confocal microscopy. It was found that the WS2/TiO2 composite layer is denser and has a lower friction coefficient when the adding concentration is 10–20 g/L. The WS2/TiO2 composite layer in situ prepared by plasma electrolytic oxidation is a new method to improve the trilogical hehavior of TC4 alloy.