The present invention relates to a solid-liquid separator for excrements of domestic animals for separating excrements of domestic animals into a solid phase and a liquid phase. The solid-liquid separator of the present invention comprises: a drum screen type first drum screen dehydrator (10) which is hollow therein and rotates at low velocity; a screw compression type second screw compression dehydrator (20) which forms a stage with the first drum screen dehydrator; a safe water level sensor (40) for sensing the water level of a solid part flowing into the second screw compression dehydrator; an automatic washer(50) for spraying water at the outside of the first drum screen dehydrator; a treatment water storage tank (60) for collecting the treatment water discharged from the first drum screen dehydrator and the treatment water discharged from the second screw compression dehydrator to discharge the same outside through a treatment water discharge hole (62); and a control portion for receiving the signal of the safe water level sensor to control whether the solid-liquid separator is operated.