Solar building heating system

A solar building heating system comprises a heat collector, a water tank and a heating heat exchanger. A water supplying pipe is connected between a water inlet of the bottom of the heat collector and a water outlet of the top of the side wall of the water tank, a water supplying water pump is arranged on the water supplying pipe, a temperature inductor used for controlling starting and stopping of the water supplying water pump is arranged in the heat collector, a water return pipe is connected between a water outlet of the top of the heat collector and a water inlet of the bottom of the side wall of the water tank, a water return branched pipe is arranged on the side wall of the water return pipe, an infloat switch and a water return branched pipe electromagnetic valve are arranged on the water return branched pipe in an up-down mode, a water recession pipe is connected between the water supplying pipe and the water return pipe, and a water recession electromagnetic valve is arranged on the water recession