In order to clarify the growth mechanism of Y123 film in the MOD process using TFA, TEM observation of the quenched samples during the growth, and measurement of the growth rate under several different conditions were carried out. TEM observation showed that the Y 2 Cu 2 O 5 , BaF 2 and CuO are converted into Y123 by release of HF due to supplying H 2 O at the reaction interface. The MOD TFA process using the multi coating method was applied to form thicker Y123 films on LaAlO 3 substrates, and the growth mechanism for the Y123 crystallization was investigated. In order to evaluate the growth rate, the electrical resistance of the precursor films during the crystallization was measured by the DC 4 probe method. It was observed that the growth thickness of the Y123 linearly increases with increasing annealing time. This result suggests that the growth rate is not limited by the HF diffusion in the precursor film. According to the gas flow rate dependence of the growth rate, it was suggested that the growth of Y123 films in this process might be limited by both the HF diffusion in the boundary layer and the interface kinetics. Then, the growth model, which includes the two limiting systems, was proposed. This model reveals a basic idea of the mechanism to determine the steady state growth rate.