Rockfall is an important geo-hazard of mountainous area in Japan and has gained greater attention and recognition due primarily to the severe accidents and mortalities happening in roadways and railways. Rock fall countermeasures are classified into preventive works and protectors. In rock protectors that have high rigidity, there are rock protecting fence, rock protecting wall and rock shed, etc. On the other hand, there is a pocket type rock net which excels in the application condition of the topography and absorbs energy by deforming itself. The standard absorbable energy of the pocket type rock net is 100 kJ. Then, the rock net is designed so that the absorbed energy exceeds the falling rock energy. However, in recently, many types of rock net such as high energy type and long span type have been developed, and there are cases where conventional design methods cannot be applied. In this study, the performance of a long span pocket type rock net was evaluated by dynamic analysis. Firstly, the physical properties of the rock net members were identified by comparing the results of the real scale field experiments with the dynamic analyses. Then, the relationships between the displacement of the net and the net width, the maximum tensional force of a horizontal rope and the rope position, etc. were evaluated by the dynamic analyses. Typically, these evaluations by conventional design methods are laborious and are carried out using the results of real scale field experiments. However, the current study revealed that the predictions by the dynamic, numerical analyses showed the validity of the performance evaluation by this means.