The invention provides an energy consumption analysis method and device after heat source transformation of an air heater of a thermal power plant. The method comprises the following steps of: calculating the mass flow of the primary air and the mass flow of the secondary air according to the rated load of the unit; achieving the constant-pressure specific heat capacity of the primary air and theconstant-pressure specific heat capacity of the secondary air ; calculating the maximum temperature rise value of the cold primary air and the maximum temperature rise value of the cold secondary airbefore the heat source of the air heater is transformed, and the maximum temperature rise value of the cold primary air and the maximum temperature rise value of the cold secondary air after the heatsource of the air heater is transformed, and calculating the steam extraction heat of the replaced steam turbine after the heat source of the air heater is transformed; calculating the change amount of the heat consumption of the steam turbine caused by the extraction heat of the replaced steam turbine after the heat source of the air heater is transformed; calculating the change amount of the electric power of the thermal power plant and the change amount of the water consumption of the desulfurizing tower before and after the heat source of the air heater is transformed; and acquiring the energy consumption change amount before and after heat source transformation of the air heater. According to the method, the energy consumption change amount before and after heat source transformationof the thermal power plant can be analyzed, and the method is simple.