Specific walking velocity, stability and energy consumption (i.e. walking characteristics) can be obtained by adjusting control parameters of complaint actuation which is essential for a passive walking robot to make full use of its own parameters to walk. In this paper, the series elastic actuator is used as the complaint actuator to adjust the walking characteristics. A passive dynamic walking model and a physical prototype with only one hip actuation were built to investigate how the control parameter can affect the walking characteristics. We studied the effects of control parameter on walking characteristics of a passive dynamic walker with torso by both numerical simulations and physical prototype experiments. The results showed that the control parameter k_p has marginal effect on walking speed but can affect the walking stability and energy consumption greatly.