In this study,the self-compatibility and mechanism of self-pollination in Hyoscyamus niger were nvestigated in the field.The results showed that:(1)The flower was incompletely protogynous,stamen elongation was the main floral mechanism which to maintain the mixed mating system.(2)Pollination control treatments suggested the species was self-compatible and has autonomous self-pollination ability.The autonomous selfing occurs at the late floral stage which overlaps with the time of stigma and anthers contacting.(3)The contact of anthers and stigma when pollen was viable and stigma was receptive resulted in delayed selfing in this species.H.niger not only select the flower structure that adapt to outcrossing,but also promoting self-pollination through stamen elongation.These results indicate that H.niger has a well developed capacity for delayed selfing,which provided reproductive assurance in the study population.