The invention discloses flux paste special for unleaded tin-bismuth solder. The flux paste special for the unleaded tin-bismuth solder comprises, by weight, 10-20 parts of hydrogenated rosin, 5-10 parts of disproportionated rosin, 10-15 parts of dimer rosin, 5-10 parts of tetrahydrofurfuryl alcohol, 5-10 parts of pentaerythritol, 5-8 parts of butyl cellosolve, 5-8 parts of octyl ether, 5-8 parts of dibasic acid esters, 2-5 parts of phthalic acid dibutyl esters, 2-3 parts of oleyl alcohol polyoxyethylene ether, 3-6 parts of polyamide modified hydrogenated castor oil, 2-4 parts of succinic acid, 1-2 parts of pyridine hydrochloride, 1-2 parts of bromic acid tributylamine, 4-8 parts of DIACID 1550 and 1-3 parts of N,N,N,N'',N''-pentamethyldiethylenetriamine. The flux paste special for the unleaded tin-bismuth solder is good in wettability, the welding defect is lower than that of existing flux paste for the unleaded tin-bismuth solder, organic acid and polyamine decompose and volatilize in the welding process, the amount of residues generated after welding is small, and protective films can be formed on the surfaces of welding points through the used rosin.