A displacement sensing device is configured for a peritoneal dialysis system. The peritoneal dialysis system includes a housing and a syringe. The syringe is disposed on the housing and has a push rod. The displacement sensing device includes a guide rod, a probing module, and a resistance scale. The guide rod is coupled to the push rod, and the probing module is disposed in the housing and is fixed at the guide rod. The resistance scale is disposed at a side of the probing module. The probing module is configured to contact the resistance scale to obtain a resistance value of the resistance scale and determine a displacement magnitude of the push rod. In addition, a peritoneal dialysis system is also mentioned.