An object of the present invention is to provide a method for producing a cross-linked polyvinyl acetal resin, which can provide a cross-linked polyvinyl acetal resin having high mechanical strength and excellent solvent resistance by a simple method without a cross-linking agent, and can solve such problems as sheet attack, insufficient strength, and instability of viscosity for a long-time storage, and another object of the present invention is to provide a cross-linked polyvinyl acetal resin produced by the above method for producing a cross-linked polyvinyl acetal resin. The method for producing a cross-linked polyvinyl acetal resin comprises the step of irradiating a polyvinyl acetal resin at least having structural units represented by the following formulas (1) to (4) with ultraviolet light having a wavelength in a range of 200 to 365 nm, wherein R1 represents a hydrogen atom or a C1-C20 hydrocarbon group; and R2 represents a group having two or more functional groups, the two or more functional groups each selected from the group consisting of the functional groups represented by the following formulas (5), (6), and (7).