LNG ambient air vaporizer (AAV) composed of fin tube bundle is widely used in small to medium gas stations due to its advantages in energy and economic savings. The heat transfer of the fin tube in the bundle is affected by the adjacent fin tube, which is different with the fin tube in the large space. The heat transfer difference of each fin tube in the bundle is generally neglected during the design process, which results in large error. The heat transfer performance of the fin tube bundle of AAV was investigated. The fluid solid coupled heat transfer of the fin tube bundle was numerically simulated integrally, and the mixture model and Lee model were used to solve the vaporization process of LNG. The heat transfer coefficients of the air side of the different fin tube in the bundle were obtained, and the formula of the heat transfer difference among the fin tube bundle was obtained based on the numerical results. A field test of the LNG ambient air vaporizer was carried out in a LNG gas terminal to validate the formula.