With the fast development of a micro-extraction system, the need for development and systematic study on microseparators is growing. In this study, a T-shaped microseparator was designed to separate the droplet flow in microsystems. The separator is simple and easy to assemble with tubular microsystems. Several systems with interfacial tensions ranging from 3.36 to 48.09 mN/m were selected for separation. By modifying the surface property of the outlet capillary, the separation is adjusted from gravity-based to wettability-based. A unified mathematical model was established to describe the necessary conditions for 100% separation in both the two types of separation processes. Based on the model, the effect of operating conditions, fluid physical properties, and separator dimensions on separation performance was investigated. It was also found that the pressure control of the outlets is a key factor for 100% separation. The pressure balance between the two outlets was achieved through withdrawing the organic phase at the outlet with the feeding rate, which was proved to be reliable. With a separator diameter of 1000 mu m, the maximum throughput range of 0-4400 mu L/min was achieved for 100% separation, which covers the normal flow rate range in microsystems.