A mid-deep geothermal well inner heat exchange heating system is disclosed. A well inner heat exchanger is placed in a geothermal well, the outlet of the well inner heat exchanger is connected with anevaporator of a water source heat pump, a primary side variable frequency circulation pump is arranged on an inlet pipeline of the well inner heat exchanger, a condenser of the water source heat pumpis connected with a heating user end through a secondary side variable frequency circulation pump, the inlet of a water softening device is connected with the municipal water supply, the outlet of the water softening device is connected with a softening water tank, the softening water tank is respectively connected with a primary side pipe network circulation system and a secondary side pipe network circulation system through a variable frequency water supplement pump group. The heat exchanger is into the geothermal well, absorbs the heat of the geothermal well and recycles the heat to the ground through the circulation pump, and the heat is extracted by the water source heat pump to heat the building. The system truly achieves the way of "taking heat without taking water" to efficientlyuse geothermal energy to heat buildings, and there is no recharge problem of traditional geothermal utilization.