The invention relates to a solar energy and sewage source heat pump combined heating system. A solar water heating system and a sewage source are connected in series with the heated part of a heat pump unit through a low-temperature water tank; the heat pump unit is started at valley electrovalence at night, an evaporating end is heated from the low-temperature water tank, and heat is completely stored by the solar water heating system when working at daytime; when the sewage source heat pump unit works at the valley electrovalence, the sewage source heat pump unit obtains low-grade heat energy from the low-temperature water tank and then releases high-grade heat energy through the heating cycle of the unit; part of the high-grade heat energy is stored in a high-temperature water tank, and the other part of the high-grade heat energy is directly supplied to end equipment for heating. According to the solar energy and sewage source heat pump combined heating system, phase-change materials are added to the high-temperature water tank to enhance the heat storage capacity and heat lag capability of the high-temperature water tank; the end equipment is lower in air supply temperature by adopting a fan coil to enhance the heat supply EER (Energy Efficiency Ratio) of the heat pump unit, so that the initial investment and operating cost of the heat pump unit are reduced; and the heat of the fan coil working at daytime is from the phase-change materials inside the high-temperature water tank and the heat storage amount of water at night.