Most plant growth regulators available are synthesized and tend to be dangerous if used inappropriately. Emistim CAS is a natural plant growth regulator, with less side-effect. The research performed an assessment on Emistim CAS application in watermelon cultivation in a greenhouse. The results showed that 0.11% Emistim CAS increased reducing sugar by 15.49%, soluble solid by 13.7%, Vc content by 3.72%, titratable acid by 18.1%, and yield per hectare by 18.01%, so that watermelon quality and yield were both improved. Emistim CAS can be widely promoted in watermelon cultivation in future. Most plant growth regulators available are synthesized and tend to be dangerous if used inappropriately. Emistim CAS is a natural plant growth regulator, with less side-effect. The research performed an assessment on Emistim CAS application in watermelon cultivation in a greenhouse. that 0.11% Emistim CAS increased reducing sugar by 15.49%, soluble solid by 13.7%, Vc content by 3.72%, titratable acid by 18.1%, and yield per hectare by 18.01%, so that watermelon quality and yield were both improved. can be widely promoted in watermelon cultivation in future.