A perovskite film, method of preparing thereof, and an optoelectronic device are provided. They are prepared by steps including preparing a mixture containing a first monomer and a second monomer which can be crosslinked in situ; performing an annealing process, and the first monomer and the second monomer are reacted in situ to form a first polymer which combines with the perovskite crystal grains formed by the perovskite precursor and is concentrated at a crystal grain boundary of the perovskite crystal grains to passivate the perovskite crystal grain defects, and then a perovskite film is formed by curing.