The invention discloses an improved load calculation loop method for a gas and steam combined cycle unit. The method comprises the steps of carrying out amplitude limiting and speed limiting processing on a load command of the gas and steam combined cycle unit to obtain an actual load command of the gas and steam combined cycle unit; subtracting the actual power of a steam turbine from the actual load command of the gas and steam combined cycle unit to obtain a load command of a gas turbine; adding up a primary frequency modulation command and the load command, obtained through calculation in the second step, of the gas turbine to obtain a load command Dwref which is sent to the gas turbine finally. Due to the fact that the load calculation loop of the combined cycle unit is improved and acts on a load control system of the combined cycle unit, the response time of the system is shortened, the loading or unloading rate of the unit is increased, the problem that a traditional unit load control system can not meet newly established assessment standards is effectively solved, the number of parameters needing to be set is reduced, and the complexity of the system is reduced.