The invention discloses a gel used for skin diseases and a preparation method of the gel. The gel is prepared from carboxymethyl chitosan as a main active ingredient. The gel is prepared from the following raw materials: carboxymethyl chitosan, stearic acid, glycerol monostearate ester, potassium carbonate, triethanolamine, glycerol, paeonol and purified water. The preparation method comprises the following steps of: (1) weighing the materials; (2) taking a matrix prepared from stearic acid, potassium carbonate, glycerol monostearate ester, triethanolamine, glycerol and purified water and heating; (3) adding paeonol, stirring uniformly, thus obtaining an ointment; (4) adding carboxymethyl chitosan to purified water, stirring to be dissolved, then adding to the ointment; and (5) stirring slowly to form the gel and obtaining a product. The gel disclosed by the invention has bactericidal, anti-inflammatory, itching-stopping, scarring-reducing, skin-moistening and skincare effects, and the advantages of good stability, excellent bactericidal effect and convenience in using, and is applicable to the skin diseases of acne vulgaris, skin eczema, photosensitivity dermatitis and the like.