Fracabilty evaluation of shale gas reservoir is a key technique to improve fracturing results. Resent research of fracability assessment focuses on the effect of brittle minerals content and rock mechanical parameters as important basis for treatment section optimization of horizontal wells in shale gas formation. However，complex fracture network can only be created by connection and propagation of natural fractures. Therefore，forming condition of multi-stranded fractures constitutes the important part of the fracability assessment of shale gas reservoir，bringing more accuracy to favorable interval selection. After analyzing the mechanical condition of intersection between hydraulic and natural fractures，calculation method of initiation pressure of the multi-stranded fractures was put forward. Dilation mode of multi-stranded fractures can be established and applied as critical ingredients by dimensionless process to realize fracability synthetic assessment for shale gas reservoir based on pressure in the hydraulic fractures and in situ stress state of oil reservoir. Based on favorable interval analysis of the Longmaxi Formation on geophysics and logging data of the shale gas well，Wx2，in the southern Sichuan basin，evaluation results can determine the perforation and fracturing location. Compared with other vertical shale gas wells evaluated by conventional appraisement in this block，the test production of Well Wx2 is higher after the treatment. This case study demonstrates the reliability and practicability of the method for optimal selection of fracturing section，which can increase stimulation effectiveness and reduce treatment risk and cost.