The invention discloses a heating device for a multi-segment greenhouse and a control method. The device comprises a heat source, a water supply main pipe, a water return main pipe, a circulating water pump, a heat sink device, direct-through electromagnetic valves, four-way electromagnetic valves and temperature sensors, wherein the circulating water pump is arranged on the water supply main pipe, and water supply pipes and water return pipes in all segments of the greenhouse are connected through the four-way electromagnetic valves or direct-through electromagnetic valves to form a heating cycle. Through the combination of the four-way electromagnetic valves and the direct-through electromagnetic valves, heating of the multi-segment greenhouse is achieved, manpower and material resources are saved, the spatial arrangement of the heating device for the multi-segment greenhouse is simplified, energy consumption caused by operation of the greenhouse heating circulating water pump is reduced, and it is ensured that automatic control of the heating device is easy to achieve, and equipment operation is safe and stable in terms of design. The heating device is especially suitable for self-control greenhouses with a large number of segments and a small single-segment area.