Abstract: With headphone virtual reproduction,the influence of delay time between masker and masked signal on forward masking when sound images are virtually spatial separated in azimuth is studied.The result shows that the thresholds tend to drop by a relative large amount with the increase in delay time.Furthermore,in case of spatial separation,there are differences of thresholds,the largest one is about 15 dB.However,when masker is 70 dB,the difference of the thresholds increases a little as the delay time increases from 20 ms to 40 ms.Based on the analysis of time integration effect and basilar membrane response,the results can be explained reasonably.