The invention discloses a boron nitride-polyethylene space radiation protection composite material and a preparation method of the boron nitride-polyethylene space radiation protection composite material.The invention relates to a polyethylene space radiation protection composite material and a preparation method of the polyethylene space radiation protection composite material. The invention is used for solving the technical problem that the conventional polyethylene for preparing the space radiation protection material has low thermal stability and low efficiency of filtering protons with pure aluminum in the same mass and thickness. The preparation method disclosed by the invention comprises the following steps of: adding ethanol and boron nitride into a container, then, adding a coupling agent, and reacting in constant temperature water, so as to obtain modified boron nitride, and finally, adding the polyethylene and the boron nitride into a high mixing machine, so as to obtain the boron nitride-polyethylene space radiation protection composite material. The boron nitride-polyethylene composite material prepared with the preparation method disclosed by the invention has a thermal degradation temperature of 430-520 DEG C and high thermal stability, compared with the pure aluminum, efficiency of filtering the protons can be increased for almost 0.4-1 times, an integrated performance is excellent, and the boron nitride-polyethylene space radiation protection composite material has a wide application prospect in radiation protection of spacecrafts.