The invention discloses a series-connection sandwich-type epitaxy GaN PIN-type beta irradiation battery and a preparation method which mainly solve the problem that the energy conversion rate and the output power of a current nuclear battery are low. The series-connection sandwich-type epitaxy GaN PIN-type beta irradiation battery comprises an upper PIN junction, a lower PIN junction and a beta irradiation source layer, wherein the upper PIN junction and the lower PIN junction are connected in series; the upper PIN junction sequentially comprises an N-type epitaxial layer ohmic contact electrode, an N-type GaN epitaxial layer, a P-type SiC epitaxial layer, a p-type SiC substrate and a P-type ohmic contact electrode from bottom to top; the lower PIN junction sequentially comprises an N-type ohmic contact electrode, an n-type SiC substrate, an N-type SiC epitaxial layer, a P-type GaN epitaxial layer and a P-type epitaxial layer ohmic contact electrode from bottom to top; the beta irradiation source layer is clamped between the epitaxial layer ohmic contact electrode of the upper PIN junction and the epitaxial layer ohmic contact electrode of the lower PIN junction so that high-energy beta particles can be made full use of. The series-connection sandwich-type epitaxy GaN PIN-type beta irradiation battery has the advantages that the contact area between an irradiation source and a semiconductor is large, the utilization rate of nuclear raw materials and the energy collection rate are high, the output voltage of the battery is high, and the battery can supply power to a small circuit for a long time.