Abstract: Femtosecond laser pulses have the characteristics of ultra-short duration and ultra-high power. A series of nonlinear processes such as double photons effect, collision ionization and avalanche breakthrough will be induced, microexplosions will happen and micro-cavities will be formed at the focus in transparent materials when femtosecond laser is tightly focused into transparent materials. The micro-cavity structure induced by 25fs laser pulse in the interior of transparent materials is proposed. The energy threshold of the micro-cavity is analyzed. Three-dimensional micro-cavity dot-matrix was prepared with a three dimensional precision displacement instrument. The experiments indicate that the energy threshold for generating micro-cavity can be decreased by use of femtosecond pulse with shorter pulse width, the penetration depth of the micro-cavity can be improved by adjusting the power of femtosecond laser, the number of pulses and the beam focus, but the microcavity can not be formed if numerical aperture is too small because the tight focus can not be achieved.