Abstract: In order to ascertain the sex ratio of field population ofPhthorimaea operculella, a method based on the morphology of abdominal segments ofPhthorimaea operculella pupae was studied. The results showed that the female pupa had a long suture in the middle of the 8th abdominal segment, the suture extended to the 7th and 9th abdominal segments, it shaped as letter"Y"at the joint to the 7th abdominal segment. The long suture was formed by connecting the gonopore on the 8th abdominal segment with the oviporus on the 9th abdominal segment. The male pupa had no suture on the 8th abdominal segment, there was only a short longitudinal suture on the 9th abdominal segment. Effective pupa sexing is beneficial to monitoring dynamically the population occurrence ofPhthorimaea operculella.