The invention discloses an ultra-fast preparation method of Bi nanoparticles and surface defects co-modified BiOCl nanosheets. The preparation method comprises the following steps: (1) adding the prepared BiOCl nanosheets and a certain amount of NaN3 into deionized water, magnetically stirring the mixture for 30 minutes for uniform mixing, slowly pouring the mixture into liquid nitrogen for rapidfreezing, and carrying out freeze-drying; and (2) after the drying is finished, placing a BiOCl and NaN3 mixture in a closed high-temperature reaction kettle, filling the kettle with nitrogen protection gas, carrying out a deflagration reaction on the NaN3 by adopting a heating wire heating mode, repeatedly cleaning products by using the deionized water after the reaction is finished, carrying outdrying, and finally obtaining the Bi nanoparticles and surface defects co-modified BiOCl nanosheets. The preparation method has the advantages of short reaction time, simultaneous completion of formation of BiOCl oxygen defects and doping of Bi nanoparticles, controllable defect and doping amount, high yield and the like; and moreover, the method is simple, the operation is simple and convenient,the universality is good, and the method can be used for preparing other advanced materials.