Abstract: From the point of spatial sample, spatial interpolation for HRTF and signal mixing for multichannel surround sound are analyzed. First, it is proved that they are equivalent mathematically. Different method for HRTF interpolation is equivalent to different signal mixing method for multichannel surround sound. Then, more strict methods for deriving the signal mixing of multichannel surround sound and the law of sine of stereophonic sound are given. It is pointed out that trying to recover lateral HRTF by adjacent linear interpolation is wrong. And for accurate sound image localization, the current adjacent linear interpolation equation for HRTF is revised. At last, it is also pointed out that some methods used in the analysis of HRTF and multichannel sound can be use for reference mutually.