In order to solve the increasingly serious thermo-electric coupling problem of heating units, thermo-electrolytic coupling modes such as extraction steam condensing steam heating, low-pressure cylinder no-load heating, and high-low bypass combined heating were proposed. At present, there are few comparative studies on the electric heating characteristics and heating capacity of different thermoelectric coupling modes. Taking a 300 MW subcritical heating unit as an example, the extraction steam condensing steam heating(back pressure 14 kPa), low-pressure cylinder no-load heating(back pressure 3 kPa) and the high-low bypass system combining with heating mode were modeled by using Aspen Plus V11 software. The electric heating characteristics, thermodynamic properties of the unit were compared and analyzed by using the method of variable working condition calculation. The results show that under the condition of the same main steam flow, the maximum heating and steam extraction capacity of low-pressure cylinder no-load heating mode is about 185 t/h higher than that in extraction steam condensing steam heating mode. The ratio of steam intake from the high-parameter expander to the steam turbine intake (abbreviated as steam intake ratio) has a greater impact on the maximum heat-to-electricity ratio of the high-low bypass heating mode. When the main steam flow remains constant, the maximum heat-to-electricity ratio of the high-low bypass heating mode increases with the increase of the inlet steam ratio. Compared with the extraction steam condensing heating mode and the low-pressure cylinder no-load heating mode, the maximum heat-to-electricity ratio increased by 1.981 and 1.227 times respectively. When the main steam flow is the rated value, the standard coal consumption of generating unit calculated by the equivalent electricity method for the three heating modes is 311.64, 262.32 and 258.22 g/kWh respectively.