The present invention involves a type of small-sized pool and PTC heater for liquid heating. The PTC heating component of PTC heater is composed of several heating cores made of PTC ceramic material, completely eliminating fire risk. Meanwhile, PTC heating component external is equipped with at least one layer of insulation and sealing component, which further includes several insulation layers and at least one sealing layer outside the insulation layer, effectively eliminating electricity leakage risk. Two layers of above mentioned insulation and sealing component could meet the insulation requirements specified in IEC standard and UL standard, so it could be used for applications with large power. In addition, the PTC heater has good water route sealing ability, so it could be used for liquid heating in small size pool. The small-sized pool is equipped with PTC heater with several layers of insulation and sealing for liquid heating, safe and reliable.