The invention relates to a preparation method of a low-expansion-rate medium-temperature fuel cell cathode material, and belongs to the technical field of material preparation. The method includes the steps that firstly, polyvinyl alcohol, N,N-methylenebisacrylamide and other substances are stirred and mixed, then tetramethylethylenediamine is added, and modified hydrogel is obtained; then, Ba(NO3)2, Co(NO3), Ni(NO3)2 and other substances are mixed, heated and concentrated, concentrated liquor is mixed with the modified hydrogel, and mixed modified gel liquor is obtained; then, the mixed modified gel liquor is mixed with pretreated crushed pig bones, and roasting is carried out; finally, the mixture is pressed and roasted, and the low-expansion-rate medium-temperature fuel cell cathode material can be obtained. The low-expansion-rate medium-temperature fuel cell cathode material prepared through the method is low in expansion rate and has high matching with electrolyte materials, and the coefficient of thermal expansion is smaller than 23.3*10<-6>K<-1>; the thermal stability is high, and the service life of the low-expansion-rate medium-temperature fuel cell cathode material can be prolonged.