Online shopping has become a new shopping style. There is little research about online impulsive buying (OIB). We develop the questionnaire of the reasons for OIB by open and structured questionnaires. There are all about 327 participants took part in our survey, of which 102 participated in the open questionnaire and another225 participated in the structured questionnaire. Based on content analysis, we found that the reason for OIB includes four factors: perceived usefulness, price, entertainment and interpersonal interaction. Internal consistency analyses and CFA (Confirmatory Factor Analysis) showed the questionnaire had high reliability and validity.