The pressure (or stress) wave generated by focusing a femtosecond laser pulse inside a glass has been considered one of the important factors in determining structures created in the laser focal region. In this paper, a method of the transient lens (TrL) analysis was proposed to characterize the pressure wave. Experimentally, the TrL signal exhibited damping oscillation within 2 ns. Simulations of the TrL signal showed that the shape of the oscillating signal depended on the width and amplitude of the pressure wave. Comparing the observed TrL signal with the simulated one, we estimated these properties of the pressure wave generated after femtosecond laser focusing inside a soda-lime glass.