Abstract: Aiming at the problem that the operating environment of the solar-air source heat pump composite heating system is complex and changeable, and the fuzzy control domain cannot be adjusted in real time, a fuzzy control method of variable domain is proposed for the temperature control of the composite heating system. Taking the difference between the actual temperature and the target temperature as the input variable, and the frequency of the variable frequency pump as the output variable, the expansion factor is introduced to change the discourse domain, and the parameters of the expansion factor are optimized by the particle swarm optimization algorithm. The Matlab/Simulink simulation comparison test shows that compared with the traditional fuzzy control, the control accuracy of the method is improved by 18.39%, and the system energy consumption is reduced by 9.22%.