A gas diffusion layer, a preparation method therefor, a membrane electrode assembly and a fuel cell. The gas diffusion layer comprises gas diffusion layer substrates (41, 42) and a microporous layer slurry coated on the gas diffusion layer substrates (41, 42). An additive that contains catechol or contains a catechol structure compound is specifically added into the microporous layer slurry, and the additive is specifically dopamine hydrochloride.