Abstract: Hobbing the middle hardness surface gears with Hss tools is one of the important machining methods. This paper introduces the experimental results of cutting forces in the gears bobbing and discusses the effect of cutting conditions on the cutting forces of bobbing process. In spite of the faet that cutting forces for bobbing the middle hardness surfuce gears （HRc36-46） are weaker than those of soft surface gears of the same material, the cutting force gradient for bobbing the middle hardness surfuee gears is much higher than that of the soft surface gears. It is suggtsted that the attention be paid to dynamic characteristics of bobbing process. Besides, the experimental result shows that it is possible to machine the middle hardness surface gears on an ordinary bobbing machine under the rational cutting conditions.