The invention provides a method for preparing sodium-zirconium-silicon-phosphorus compound solid electrolyte, and belongs to the technical field of electrochemical and new-energy materials. The sodium-zirconium-silicon-phosphorus compound solid electrolyte is prepared by adopting a simple self-propagating combustion synthesizing technology with simplicity and quickness in operation, precursor is synthesized in one step, the sodium-zirconium-silicon-phosphorus compound solid electrolyte nano-powder has a grain size of 300-600nm and uniformly distributed elements. Furthermore, the method for preparing the ceramic-crosslinked polymer flexible compound solid electrolyte adopts an in-situ polymerization technology, no solvent is added in the preparation process, the ceramic powder has good compatibility with polymer, and the prepared ceramic-crosslinked polymer flexible compound solid electrolyte has excellent electrochemical performance and thermal stability.