Abstract: The influence of temperature ratio on the penetration depth of two-dimensional confined cross flow is investigated numerically.It is found that the temperature ratio of jet to main flow was an important parameter independent of momentum ratio.This phenomena can be explained in terms of the concept of "thermal drag".A cold jet injected perpendicularly into a confined hot air flow is heated and accelerated as the momentum ratio is given.The thermally induced pressure drop is converted into the momentum increase and consequently increases the penetration depth.On the contrary,a hot jet injected perpendicularly into a confined cold air flow for the given mometum ratio decreases its own momentum due to cooling by the mainflow.As a consequence,its penetration depth also is cut down.