Based on the avalanche model, the evolution of femtosecond laser induced micro-e xplosion in fused silica was investigated. The microscopic processes, including the production of conduction band electron (CBE), laser energy deposition, CBE a nd energy diffusion were solved by a finite element method in two-dimensional cy lindrical coordinates. The accumulated net charge and the electrostatic field we re also calculated. The results indicate that the CBE and energy diffusions play an important role in the micro-explosion in dielectrics.