Abstract: A kind of tuning algorithm of antenna tuner based on bi-searching and step searching is introduced through dividing the impedance complex plane. The basic conception and different stopping rules of the algorithm are analyzed and the problem called reverse tuning is also be pointed which occurred possibly in the algorithm. At last the tuning algorithm is simulated with 2.4m whip antenna in HF band for impedance matching, the effects on the algorithm performance with different searching number or stopping threshold are analyzed and the parameter values are determined according the analysis. So the algorithm can achieve the fine performance in impedance matching with fast tuning speed and nice matching precision.