Insufficient or excessive oxidation of the Spiro-OMeTAD layer can lead to a low efficiency of the perovskite solar cell. The effect of the hole transporting layer on Spiro-OMeTAD oxidation is investigated to solve such problem. Four different methods are primarily utilized to oxidize the hole transporting layers. Then, the optoelectrical performances of the hole transporting layers before and after oxidation are studied to determine the optimum oxidation method and its conditions. Subsequently, planar devices with a ITO/SnO2/CH3NH3PbI3/Spiro-OMeTAD/Ag structure are fabricated. The photoelectric properties are characterized and compared before and after oxidizing the devices. The result shows that an efficient oxidation decreases the pinholes on the surface of the Spiro-OMeTAD layer and makes it fully dense. Thus, the fill factor (FF) of the perovskite solar cell is increased. Furthermore, the oxidation treatment reduces the parasite absorption of light by the Spiro-OMeTAD layer and improves the effective optical absorptance of the perovskite solar cell. In addition, the oxygen oxidation in the Spiro-OMeTAD precursor is apparently superior to the other oxidation modes. Compared with the air-oxidized device, the FF of the oxygen-oxidized device rises from 0.43 to 0.63, and the photon conversion efficiency increases from 9.06% to 14.19% under the optimum operating conditions.