Dielectric measurements on $CsH_2PO_4$ single crystal with 1-dimensional chain-like hydrogen bonds have been performed in the frequency region below 6MHz as a function of temperature near the ferroelectric phase transition. The effects of bias fields and various probing electric field amplitudes seem to exhibit domain-state behaviours around 150K. And pyroelectric current measurement shows that there starts to appear for the contribution from the spontaneous polarization near 140K. The dielectric constant and loss curves for zero bias field were explained well by Davidson-Cole equation with a single relaxation time at temperatures very close to 150K.
