Using the generalized nonlinear Schrdinger equation, the relation between the laser parameters and the place, size of the plasma induced by a focused laser packet in transparent materials have been simulated. Calculation shows that: the ultimate density of the induced plasma trends towards a constant for a given diffraction length of the laser packet, and the region of the induced plasma becomes larger and longer with the increase of the laser power; for a given power laser packet the density of the induced plasma decreases with the increase of the diffraction length of the laser packet; for laser packets with different diffraction length the region of induced plasma extends to different direction with the increase of the laser power, which is consistent with the experimental results by Gordienko et al.. This study may be beneficial to understand the formation of the induced plasma in materials and push forward its application in laser processing.