Abstract: The flexibility reformation of the heating unit is an effective measure to break the “heat-power constraints” and realize the capacity support of the coal-fired power unit for renewable energy power generation. The most common technical solution is the steam turbine low-pressure cylinder operates under zero output condition with HP-LP bypass steam extraction or electric boiler supplying heat. For a 350 MW supercritical heating unit, we adopted the iterative calculation method of variable working conditions to compute and compared the typical operating points thermal economy of the minimum power output, maximum heat supply and heat preservation and power regulation under the two schemes, as well as the adjustable range of electric output in thermal economy of the deep peak load section. The results show that, due to the small cold source loss, the coal consumption of the electric boiler scheme is only slightly larger than that of the HP-LP bypass steam extraction scheme under the same thermal and electric load conditions. While for the good reverse electric load regulation capability of electric boiler, the adjustable range of electric load is significantly larger than that of the HP-LP bypass steam extraction scheme.