This paper presents a walking control strategy considering ground reaction force for bipedal robots. This research focuses on an unknown environment especially soft terrain. The proposed control method has two controllers. One is to control the robot balance by controlling the position of center of gravity (COG). The other is to control the position of swing leg. The COG position controller calculates force reference that is generated by the robot pushing the ground using the support leg. Then the ground reaction force is controlled to at the tip of the support leg with force controller without any environmental stiffness information. Bipedal robot walking simulations on the hard and soft grounds are also presented to show validity of the proposed controllers.