With the aid of the COMSOL program, the laminar mixed convection heat transfer in a channel-open cavity with two heat sources of constant 20 W each and varying input air velocity ranges (0.1, 0.5, 1.0, and 1.5 m/s) is numerically determined. In this study, the effect of varying inlet air velocity on the heat transfer characteristics is investigated. Numerical results show that the temperature starts to fall steadily as one moves farther and further away from the site of the two heat sources and closer to the horizontal channel. The higher the velocity of the air entering the cavity, the greater the natural convection that will be created by the heated heat sources. The increase in inlet air velocity will increase the turbulence of airflow and thus increases the pressure distribution. The increase in absolute y-direction decreases the velocity distribution. The rise in the inlet velocity of air will increase the transfer of heat; thus, the Nusselt number will be great when increasing air flow velocity. The maximum Nusselt number is at the interface and reduces with increasing the absolute value of y. A reduction in air temperature and an increase in air density result from an increase in natural convection from the cavity into the air stream caused by an increase in air input velocity.