The effects of flux components and compositions of solder alloys on the wettability of the Sn-Zn alloys on aluminum surface was investigated. The results show that the wettability of the Sn-9Zn solder on aluminum substrate improved with flux of double solvents composed of diethanolamine and triethanolamine, which is better than single solvent. When flux is composed of 3% zinc fluoborate as activator and 30% triethanolamine plus 67% diethanolamine as double solvents, the spreading area of the Sn-9Zn solder reaches to 75%. Trace addition (0.002%-0.005%) of Al results in significant improvement of the wettability of the Sn-9Zn based solder. However, additions of Bi or Sb are not beneficial to the wettability of the solder on aluminum substrate.