The WS2/P201 hybrid lubrication system was constructed with a combination of WS2 film deposited by magnetron sputtering and P201 oil. The tribological properties of the WS2/P201 hybrid system with atomic oxygen (AO) irradiation are inferior compared to WS2 film and the WS2/P201 hybrid system without AO irradiation. Mainly the effects of AO irradiation on the components and tribological performance of the WS2/P201 hybrid system were studied. AO irradiation not only leads to breakage of chemical bonds and formation and volatilization of small molecular compounds, but also triggers crosslinking reaction between molecular chains, which results in an increase of molecular weight and broadening of the distribution of molecular weight. The loose columnar crystal pores are filled with viscous oil and the S/W ratio decreases notably after AO irradiation. The lubricating and failure mechanisms of the WS2/P201 hybrid system under AO irradiation were revealed. It is found that WO3 formed during AO irradiation plays an important role in the sliding process.