Abstract: YBCO thin films with different thickness were deposited on LAO substrate by MOD method.Effect of the thickness of YBCO film on microstructure was studied by X-ray diffraction.Results show crystal orientation is improved with increasing YBCO films thickness the best value is observed at about 800nm and becomes weaker after 800nm;the lattice parameter c becomes bigger with increasing the thickness of films.Rocking curve FWHM and φ scanning of YBCO films with different thickness and reciprocal space mapping of the 800nm YBCO thin film were investigated.Results show crystallization of the 800nm YBCO thin film is better than others.Then,the effect of the thickness of YBCO film on critical current density was studied.