The invention discloses a solar heating system and a heating method thereof. The system comprises a solar heat collector, an indoor terminal, a heat storage water tank, a fluid supplementation water tank, a fluid storage water tank, a heat collection circulating pump JP, a fluid supplementation circulating pump BP, a heating circulating pump GP, a heat source circulating pump RP, a heat pump HP, an electromagnetic valve DF1, an electromagnetic valve DF2, an electromagnetic valve DF3, a water supplementation electromagnetic valve BF and a plate heat exchanger. The heating method comprises the steps of setting the temperature of the solar heat collector, controlling, adjusting and the like. The solar heating system and the heating method thereof provided by the invention have the beneficialeffects that a solar heat collecting system starts to collect heat from the low temperature being around 5 DEG C, the heat collecting efficiency is at the highest state, the solar heat energy can be collected and stored sufficiently, and the heat energy of the low-temperature section of the heat storage water tank can be sufficiently utilized, so that compared with the prior art, the heat collecting area and the volume of the heat storage water tank can be correspondingly reduced, and the occupied space is reduced. The heat at the temperature below the heating temperature can be sufficiently utilized, so that the initial investment of solar heating is reduced, and the heat energy utilization efficiency of the system is improved.