In this paper, we investigate the power control problem in mobile ad hoc network, and give out an improved variable-range transmission power control algorithm based on minimum spanning tree algorithm (MST). Using previous work by Gomez and Campbell, we show that in consider of node's mobility, the previous variable-range transmission power control based on minimum spanning tree algorithm is not suitable for mobile ad hoc network. For this reason, we give out an improved variable-range transmission power control algorithm to support node's mobility and solve asymmetric graph problem. The results of this paper enhance the possibility of using variable-range transmission power control in mobile ad hoc networks.