To improve the operating performance of a heat pump system, experimental data obtained from a solar integrated air source heat pump (SIASHP) water heater system were analysed in detail. With the information integration and decision-making abilities of data fusion, the all-weather operation strategies of the system were newly proposed. These new strategies comprehensively considered the solar radiation intensity, air temperature, energy dissipation, and COP. According to the relative magnitudes of the solar radiation intensity and air temperature, the system performed reasonably in different modes, ensuring its efficient operation under all weather conditions. Then, the annual costs of the system in five cities located in regions with various solar radiation intensities were analysed and compared. It was concluded that the maximum savings achieved by the system were $86.5/yr and $225.3 per year compared with gas and electric water heaters, respectively, indicating the system is cost-efficient and promising. Furthermore, the operating performance of the switched mode was optimized based on a regression algorithm. When the solar radiation intensity was poor and the temperature of heated water rose to 34 degrees C, the air source evaporator was switched to a solar evaporator. In addition, the COP of the system was 3.023, equal to 97% of the COP of a solar energy heat pump (SHEP) water heater with a sufficient solar radiation intensity. Therefore, the optimized scheme can compensate for the inefficient operating conditions under a weak solar radiation.