Humanoid robots are expected to perform tasks in dangerous sites such as disaster areas instead of a human. In order to reach the destination quickly, we consider throwing a humanoid robot in the parachute from the sky. It is discussed analyses of the impact acceleration and how to reduce the landing impact using a life-sized one-legged robot in this paper. The robot has a SEA (Series Elastic Actuator) in its knee and the angle of the knee is controlled by a proportional feedback controller. In order to understand the relationship between the knee angle and the impact acceleration, drop tests were conducted. The drop tests show that the peak acceleration of impact between the body and the floor was the smallest when the joint angle was 5π/12 rad. On the other hand, the peak acceleration of impact between the sole and the floor was the largest. When the joint angle is π/12 rad, the peak acceleration of impact between the sole and the floor was the smallest. In order to reduce both peak accelerations, the joint angle was set as π/12 rad at the time of landing, and then the joint moved from π/12 rad to 5π/12 after landing. It was confirmed that this motion is able to reduce both peak accelerations by experiments.