Abstract: Cryogenic target is one of the critical component in inertial confinement fusion, which is assembled inside a hohlraum needed to be filled by fill tubes. In this paper, a microchannel model is established based on the analysis of the big difference between the microchannel and the conventional channel on flow and heat transfer characteristics. The modeling is implemented with FLUENT software and the correction of Navier-Stokes equations is inserted through UDF. From the results of simulation, the effect of gravity can be neglected while that of surface tension should be taken into consideration. Velocity slip and temperature jump are also calculated for their significant influence on flow and heat transfer in the microchannel. Three different fill tube models are compared to provide a suitable type for experiment design. Choosing different boundary conditions, certain filling of fuel could be confirmed. During the filling process, the temperature and pressure of inlet should be increased gradually with the increasing temperature and pressure of outlet to guarantee continuous controlled filling.