Abstract: A new type of flux for SnAgCu lead-free solder paste was developed. The effects of composition and content of active agent in the flux on the wettability of the flux and the corrosion of the solder joint were studied. Nine organic acid surfactants were preliminarily optimized according to the morphology and spreading rate of the solder joints,and the internal relationships between the content of the three optimized organic acids and the spreading rate, morphology and corrosion of the solder joints were further studied with the spreading rate, morphology of the solder joints, residuals after welding and solder joint corrosion as the main evaluation indexes. The orthogonal experiment was designed and appropriate factor and level were selected to further compound the preferred organic acids, and the best ratio of active agents in the soldering flux was determined combined with range analysis. The results show that the combination of organic acids not only improves the spread rate and shrinkage of solder joints, but also reduces the corrosion of solder joints. When the mass ratio of A acid, adipic acid and succinic acid in flux is 2.5 ∶4.0 ∶2.5, the prepared Sn3.0Ag0.5 Cu（SAC305） lead-free solder paste has excellent wettability, the spread rate of the flux is 85.13%, the solder joint has no retraction, there are few residues after welding, and the corrosion of the solder joint is small.