In order to investigate characteristics of bubble deformation in immiscible fluids, the bubble shape change during the interface and the relationship between aspect ratio(E) and dimensionless number of forces is obtained. A three-dimensional model is established and the free-floating behavior of a single bubble in immiscible fluids is numerically simulated by phase-field method. The simulation results are in good agreement with experimental results. The research shows that, in the lower liquid, the relationship between E and We, Ta, Re is distributed between two intersecting lines. In the upper liquid, the relationship between E and We, Ta, Re is distributed between two parallel lines. Comparing the bubble deformation and the influence of the forces. Compared with gravity, the inertial force plays a leading role in the bubble shape in the lower liquid and upper liquid. Compared with the viscous force, the surface tension dominates the bubble shape in the lower liquid.