In order to better understand the effect of the wettability between Cu and W on the infiltration process during the fabrication of CuW alloy, the flow patterns of molten Cu in the W microchannel at four different contact angles between Cu and W were simulated by finite volume method based on the modified Navier–Stokes equation, and the effect of Co content in molten Cu on the flow front was studied as well. The results show that the less contact angle between Cu and W increases the differential and negative pressures generated at the flow front and thus increases the flow velocity and decreases the infiltration time during the fabrication process of CuW alloy. However, the less contact angle is easier to cause a larger negative pressure with the progress of the infiltration process, which is not favourable for the filling of molten Cu in the W channel. In addition, Co addition can accelerate the flow of molten Cu in the W channel due to the increased differential pressure.