Abstract: High combustion chamber pressure engine scheme is to be used in new generation of liquid rocket engine with propellant LOX/hydrocarbon.For this kind of engine thrust chamber cooling is one of key technical problems.An optimal design method for geometric size of regenerative cooling channel is provided.The minimum of cooling pressure loss has been taken as an optimal objective.The results of a typical calculation show t hat the cooling pressure loss may be decreased 50% by using the optimal method.