The invention relates to a three-dimensional space structure modeling and key block identifying method of engineering rock mass, belonging to the fields of modeling and analysis of the entity structure of the rock mass engineering such as geotechnical engineering, mine exploitation, engineering construction, hydraulic engineering, underground structure and the like. The method of the invention comprises the following steps: (1) acquiring the structure original data of the engineering rock mass in the field; (2) processing and extracting the original data of the engineering rock mass; (3) constructing the model of the engineering rock mass; and (4) identifying blocks. The invention has the advantages as follows: the method realizes the purposes of quickly searching the structure of the engineering rock mass and identifying the key blocks, considers the requirement for quickly identifying a new structural surface in the engineering implementation process, and can be used for automatically searching the key blocks and counting the amount of movable blocks.