The mechanical behavior of capsule in microscale flow is fundamentally important in physiology, pharmaceutical or agricultural industries, fluid mechanics and physics. In the present paper, the performance of two-dimensional capsule in time-dependent microchannel flow is investigated by a numerical simulation method, which combines the finite volume method for solving the fluid problem with the front tracking technique for capturing and tracking the capsule membrane. Initially circular capsule is considered in the simulations, and the capsule is modeled as liquid medium enclosed by a thin membrane, for which linear elastic properties are taken into consideration. The membrane mechanics is adopted to calculate membrane-fluid interaction, based on which the solution of fluid problem is obtained. The capsule membrane is advected explicitly according to fluid velocity results. Results of capsule position, capsule moving velocity, capsule shape, velocity field of fluid inside and outside the membrane can be obtained from the numerical simulations. Based on these results, the effects of time-dependent background fluid on capsule behavior are studied.