Abstract: In this paper,by considering higher order approximation to the interaural phase difference,a more general localization equation for stereo sound image with interchannel phase difference is derived.At very low frequency or low interchannel phase difference,this equation can be simplified to the result of Makita theory.But in general condition,image position is obviously affected by frequency.It is shown that image position varing with frequency is the main reason for image width broadening in stereo reproduction with interchannel phase difference.And an extra interaural sound level difference caused by interchannel phase difference is the main reason for image naturatness degrading.In practice,it is necessary to reduce the interchannel Phase difference,at least,to less than 60°.