YBCO superconducting films with Tc of 90 K were prepared via fluorine-free polymer-assisted metal organic deposition (PA-MOD) on (001) LaAlO3 single crystal substrate. The influence of different firing temperatures and gas humidities during high-temperature heat treatment was investigated to fabricate high performance YBCO films. The degree of biaxial texture for the films by different heat treatments was analyzed by X-ray diffraction θ-2θ scan, ω scan and φ scan. Surface morphologies were studied by scanning electron microscopy (SEM). Magnetic moment versus temperature curves and magnetic hysteresis loops were measured by Quantum-Design SQUID XL (7 T). The results show that the YBCO film fired at 770 oC in dry gas has excellent biaxial texture as well as smooth and dense surface morphology. The YBCO film prepared by this optimized treatment has critical current density Jc of 2 MA/cm2 (77 K, self-field) which is 1.7 to 6.7 times of that for YBCO films by other heat treatments.