The invention discloses a micro-analysis method applied to the rock material I type crack initiation and expansion process. The method comprises the following steps that 1, a micro model for SiO2 crack initiation is built; 2, the working condition is set, and the crack expansion process is simulated and analyzed, and the average stress and the total crack length of the area at one end of a crack are calculated; 3, a crack stress intensity factor is calculated; 4, crack initiation driving force is calculated; 5, a calculation method of the average speed of microscopic crack expansion is built;6, influence rules of different conditions to the crack initiation and expansion process are analyzed. The method has the advantages that it is first put forward that molecular dynamics is adopted forsimulating the rock material microcrack initiation and expansion process, the stress intensity factor calculation method under microscopic molecular dynamics simulation and crack expansion speed calculation method in microscopic simulation are built, and a theoretical basis is provided for deeply analyzing the whole microcrack expansion process such as rock brittle fracture and creep and mechanism study.