The influence of the hysteretic behaviour in reactive sputtering with a pure aluminium target in the presence of argon and oxygen plasma on transmittance and surface free energy of aluminium oxide films was investigated by plasma optical emission spectroscopy technology. The evolutions of aluminium, and aluminium oxide emission lines as functions of oxygen flow rate at constant power and pressure were studied. A steep transition from the metallic sputtering to the compound sputtering was observed upon increasing the oxygen flow rate from 0.0 SCCM to above 2.0 SCCM. Then an optimal deposition zone was obtained through analyzing the hysteretic curves of aluminium and aluminium oxide emission lines. The evolution of crystal structures of samples was discerned by X-ray diffraction spectra data. Energy dispersive X-ray spectroscopy data also demonstrate the relationship between the chemical compositions of aluminium oxide films and the hysteretic behaviour. The film deposited between 1.5 SCCM and 2.0 SCCM oxygen flow rate displays an optimal and stoichiometic atomic ratio of O to Al and mass ratio of O to Al. The changes in the transmittance of samples were discovered to depend on the oxygen flow rate by UV-VIS transmittance spectra, and the changes in surface free energy were studied by contact angle measurement. The influence of the hysteretic behavior in reactive sputtering with a pure aluminum target in the presence of argon and oxygen plasma on transmittance and surface free energy of aluminum oxide films was investigated by plasma optical emission spectroscopy technology. The evolutions of aluminum, and aluminum oxide emission lines as functions of oxygen flow rate at constant power and pressure were studied. A steep transition from the metallic sputtering to the compound sputtering was observed upon increasing the oxygen flow rate from 0.0 SCCM to above 2.0 SCCM. Then an optimal deposition zone was obtained through analyzing the hysteretic curves of aluminum and aluminum oxide emission lines. The evolution of crystal structures of samples was discerned by X-ray diffraction spectra data. Energy dispersive X-ray spectroscopy data also demonstrated the relationship between the chemical compositions of aluminum oxide films and the hysteretic behavior. The film deposited between 1.5 SC CM and 2.0 SCCM oxygen flow rate displays an optimal and stoichiometic atomic ratio of O to Al and mass ratio of O to Al. The changes in the transmittance of samples were discovered to depend on the oxygen flow rate by UV-VIS transmittance spectra, and the changes in surface free energy were studied by contact angle measurement.