The invention relates to a radio-voltaic nuclear battery based on perovskite crystals and a preparation method thereof. A nuclear battery structure sequentially comprises a radiation source, an anodeelectrode, a p-type perovskite layer, an intrinsic perovskite layer, an n-type perovskite layer and a cathode from top to bottom. In the nuclear battery structure, the radiation source emits high-energy particles such as beta particles, X rays and gamma rays, the high-energy particles are absorbed in the high-thickness intrinsic perovskite layer, and photo-induced electron/hole pairs are generatedthrough a photoelectric effect. The p-type perovskite layer, the intrinsic perovskite layer and the n-type perovskite layer form a PIN structure, and the PIN structure forms a depletion layer. Due toa built-in electric field of the depletion layer, photo-induced electrons/hole pairs generated by the high-energy particles are separated and drift towards the cathode and the anode respectively to form open-circuit voltage or short-circuit current.