Abstract: The Human Error Probability (HEP) quantification methods are reviewed. Firstly, the basic concept of HEP is introduced and the necessity for quantify HEP is emphasized. It is pointed that the HEP quantification is not only an important ingredient of Probabilistic Risk Assessment (PRA) for human-machine system, but also can provide a significant guidance for human error reduction. Secondly, considering that there are differences in the theoretical basis of each HEP quantification method, the current HEP quantification methods are categorized into three types; they are time-based, task-based, and context-based. The typical methods of each type are analyzed in details in term of their basic ideas, quantification processes, their developments, and applications. Lastly, the HEP quantification methods are reviewed from aspects of the usage of human error data, the representation and application of scenario, the models used in quantification process, the goal and result of quantification. Some propositions are provided.