The invention discloses melatonin soft capsules and a preparation method thereof. The contents of the soft capsules serving as the product comprise melatonin, polyethylene glycol and stabilizer in a weight ratio of 1:60-360:2-12, wherein the soft capsule shell comprises gelatin, pure water, glycerol, D-sorbitol solution, titanium dioxide and lemon yellow in the weight ratio of 1.0:0.76-0.85:0.45-0.55:0.15-0.25:0.002-0.006:0.00008-0.00024; the product is the melatonin soft capsules with polyethylene glycol as medium; a certain proportion of stabilizer is added into the contents; and the components such as the D-sorbitol solution and the like are added into the capsule shell. The product can solve the problems that the melatonin in the contents of the soft capsules available on the current market is easy to migrate, the capsule shell is easy to become hard and crisp and difficult to break down after being placed for a long time and the like.