The present invention relates to the technical field of medicine, in particular to a conjugate of dezocine and polyethylene glycol and a pharmaceutical composition thereof. The conjugate of dezocine and water-soluble oligomer provided by the present invention has better pharmacokinetic properties and a high drug absorption degree, may reduce the side effects of the drug, and achieve a smaller administration dosage and a more diverse mode of administration, such as oral administration, in clinic. Compared with dezocine, the conjugate of the present invention has a stronger analgesic effect and a longer analgesic duration, may reduce the frequency of drug administration, improve patient compliance, and has advantages in effectiveness and safety of the drug, as well as drug tolerance, etc.