Environmental conditions like solar irradiance and ambient temperature affect the operation performance of multi-heat sources solar assisted heat pump water heater greatly. Under bad weather condition, the energy consumption increased fast, leading decreased total thermal efficiency of the system. Solar collector in the system would become heat sink in too low solar irradiance or ambient temperature. In order to avoid this situation and improve the system performance, an operation control method was proposed. A numerical simulation study of the modified system was correspondingly carried out. The results were analyzed and compared with previous ones, which showed the system could reduce energy consumption achieving much better performance after modification. The improved operation performance of HP+SC mode and SC+HP mode was compared too. The results showed the former always had higher COP and lower EFFT but achieved performance enhancement more obviously.