Abstract: Based on the phase-field method, the problem of two-phase flow in a micro-fluidic device and the interaction of the fluid components with a wall are discussed, and the transport equations for the two-phase flow given. Then, a numerical technique to solve equations for micro-fluidic quadrate devices is proposed by the finite difference method, and the numerical simulation of the flow and deformation of a droplet and multiple droplets in a cubic pipe demonstrated. It is found that the dimensionless constants Pe, C_</em>a are important parameters, and affect the deformation of the droplet. The deformation of the droplet increases with high Pe. If the parameter C_</em>a is between 0.35 and 0.50, the curvature at the end of the droplet decreases gradually from a positive value to negative, and become concave at the end.