The invention discloses soldering paste and a soldering flux thereof, and preparation methods thereof. The soldering paste comprises lead-free soldering powder and the soldering flux, wherein the soldering flux comprises the following raw materials in percentage by weight: 6-15 percent of polyisobutene or polybutylene, 3-10 percent of imidazoles compound, 15-45 percent of rosin, 3-15 percent of thixotropic agent, 3-15 percent of active agent and the balance of solvent; therefore, through adding at least one of polyisobutene or polybutylene and replacing partial rosin with the polyisobutene orpolybutylene, on the one hand, the consumption of the rosin can be reduced so that yellow rosin residuals are reduced, on the other hand, the polyisobutene or polybutylene residuals are both colorless and transparent viscous fluid and can soften the harder rosin residuals so that soldering paste residuals are soft, colorless and transparent substances, therefore, the probe test passing rate is greatly improved, and an effective guarantee is provided for the welding quality of electronic products.