This paper evaluates fixed step algorithm of closed loop power control and investigates an optimum step size for WCDMA communication employing high altitude platforms (HAPs). In CDMA, power control must be used to overcome near-far effect, shadowing and multipath fading. Users who are distributed within HAPs coverage will have different channel characteristic depending on their elevation angle. Therefore, parameter of power control algorithm should be designed to comply with the channel characteristic. Step size is one parameter in fixed step closed loop power control that will be investigated in this paper. Considering the measured HAPs channel characteristic, this paper investigates an optimum step size that will resulting a minimum power control error (PCE). Computer simulation shows that optimum step size depends on user's elevation angle. The higher the elevation angles the smaller the optimum step size of the power control.