The assisting gas jet emerging from a conical nozzle and impinging onto a three-dimensional slot resembling laser cutting is examined. The flow and temperature fields around the slot are predicted numerically, incorporating the control volume approach. The Nusselt number and the skin friction variation due to different assisting gases, including helium, nitrogen, and air, are predicted at slot walls. The model study includes the three-dimensional modeling of turbulence flow field around the slot. It is found that the assisting gas type has significant effects on the Nusselt number and the skin friction at the slot surface: the Nusselt number reduces significantly while the skin friction increases considerably for helium assisting gas.