Electric square pulse was used to study the polarization dynamics in $KH_2PO_4$ single crystal near the Curie Point. The temperature $T_f$ at which the crystal becomes unstable was observed to be higher than the phase transition temperature $T_c$ by 10.6 degrees. It was found that the dynamics of polarization saturation between $T_f$ and $T_c$ was more complicated than the simple relaxation. The present work favours the conclusion that the ferroelectric phase transition of $KH_2PO_4$ crystal is of the first order.
