The invention relates to a preparation method of 
tiamulin base. The preparation method includes: filtering pleuromulin 
fermentation broth, 
drying mycelium, performing leaching by using 
methanol as 
solvent, using 
acetone to extract leach liquor after vacuum concentration, concentrating extract, transferring concentrate into a synthetic reactor, adding paratoluensulfonyl 
chloride, allowing for synthetic reaction at pH of 11-12 and 
reaction temperature of 20-30 DEG C, allowing for standing and layering after complete reaction, adding 
tetrabutylammonium bromide and diethylaminoethyl mercaptide into 
ketone phase respectively , allowing for full reaction at pH of 9-10 and the 
reaction temperature of 50-60 DEG C, adding water for extraction, discarding aqueous phase, filtering the 
ketone phase, and reducing the original volume to 60-70% by vacuum concentration to obtain 
tiamulin base. The original process is improved, the salifying and 
crystallization process is omitted, the 
tiamulin base is used to produce preparations directly, and accordingly equipment 
investment cost and production cost are lowered, product quality is improved, and the content of tiamulin base reaches 80-90%. Organic solvents used in the preparation method are recyclable, environmental 
pollution is reduced, and the preparation method has promising development prospect.