The invention discloses a sunscreen with high sun protection index and a preparation method thereof. The sunscreen comprises the following raw materials: water, ethyl hexyl methoxycinnamate, bis-ethylhexyphenol methoxyphenyl triazine, dioctyl carbonate, coco-caprylate/caprate, octocrilene, propylene glycol, diethyl hydroxybenzoyl hexyl benzoate, glycerinum, methylene bis-benzotriazolyl tetramethylbutylphenol, decyl glucoside, propylene glycol, xanthan gum, sucrose polystearate, cetachiol stearate, butanediol, ethyl hexyl triazinone, phenoxyethanol, octyl glycol, sodium polyacrylate, tocopherol acetate, bisabolol, sodium stearyl glutamate, polydimethyl alcohol siloxane, sodium hyaluronate, EDTA (ethylene diamine tetraacetic acid) tetrasodium, glucomannan, black tea fungus membrane dispersion, and microcrystalline cellulose. The sun protection and the durability of the sunscreen with high sunscreen index are improved by adopting glucomannan, black tea fungus membrane dispersion and microcrystalline cellulose as a reinforcing system.