Human reliability analysis (HRA) has become a necessary part of probability safety analysis (PSA). Analysis for human error initiating event (category B human error events), as an important part of HRA, were not ever formally reported. This paper expounds the definition and classification of category B human error events. A basic analysis procedure and method , which has been used in the HRA of a nuclear power plant, is established. Category B human error events of WANO 940 operating events and of a domestic nuclear power plant operating events are analyzed statistically and sought for their r...