A preparation method of composite blue luminescent thin film of sulfonated poly(p-phenylene) (i.e. poly[2,5-bis(3-sulfonatopropoxy)-1,4-phenylene-alt-1,4-phenylene]) and LDHs (Layered Double Hydroxides) is disclosed. The preparation method comprises the following steps: preparing delaminated LDHs colloidal solution using formamide solvent, preparing sulfonated poly(p-phenylene) aqueous solution, and performing alternate assembling on hydrophilically treated substrate in the two solutions to give the composite thin film of sulfonated poly(p-phenylene)/LDHs multilayer. The preparation method has the advantages of simple preparation process, and film thickness controllable at nanoscale precision, in addition, this method also achieves the immobilization of luminescent polymer via restricted space among LDHs layers and host-guest interaction, effectively improves thermal stability, and reduces fluorescence quenching caused by aggregation.