In order to apply to analysis methods of mechanism and cross tabulation methods for the influence factors by the accident types to the object of accidents which occurred in R. C and P. C methods among the accidents in construction work sites, the latent hazards in P. C method are evaluated from the data of accidents in H Company from Jan. 1, 1993 to Dec. 31, 1993. The relationship between accident types and unsafe acts, unsafe conditions are recognized and the hazards of R. C method and P. C method are compared from the data acquired by the analysis of causes for a kind of occurrence mechanism. In conclusions, the items such as causes of accidents, accidents types, occurrence time, and the characteristics, are concentrated on one side in the P. C method, which is quite different from R. C method. Therefore the control method for the accident causes is easily established with a lot of effective advantages. The frequency and severity of accidents in P. C method are so low in comparison with R. C method.