The invention relates to a gas-steam combined circulation unit speed-regulating system model and a model establishment method thereof. The method includes the steps that according to data which are measured according to modules and steps, the proportional coefficient and integral coefficient of the PID step are recognized; according to actually measured data which are obtained through performing valve position instruction phase step testing on a pre-mixing valve, a diffusion valve, a duty valve and an IGV valve, the servo card proportion magnification time, full-opening time and full-closing time of execution mechanisms of the pre-mixing valve, the diffusion valve, the duty valve and the IGV valve; according to gas turbine power, steam turbine power, combined circulation unit overall power, combined circulation unit gas turbine exhaust temperature and other actually measured data, a combustion chamber time constant, a steam turbine inertia time constant and a boiler inertia time constant are obtained through recognition; according to closed-loop frequency disturbance actually measured data, all step parameters of a generator set speed-regulating system are recognized; the obtained parameters are optimized, and a model response is calculated. The method is beneficial to perform actual measurement model establishment on the gas-steam combined circulation unit speed-regulating system rapidly and accurately.