SrTiO3(STO) thin films are manufactured on LaAlO3 (100) substrates by pulsed laser deposition (PLD) with different partial pressures of oxygen. The films′ microstructure, surface morphology and optical characteristics are characterized. In accordance with the above results, the partial pressures of oxygen is an important process parameter for the preparation of STO thin films by PLD. With decreasing partial pressure of oxygen, the crystallinity of the thin films has ameliorated, and the structure changes from cubic to tetragonal. Film grain size gradually increases, film grain number and film thickness decrease when the partial pressure of oxygen rises. The STO films present a low optical absorption in the 400~2500 nm wavelength range. The band gap energy of the STO films deposited at 5, 10 and 15 Pa are 3.84, 4.13 and 4.05 eV, respectively. This can provide good experimental data to the further analysis of STO thin films.