The invention discloses a low-temperature high-power lithium-manganese battery and a preparation method thereof, the low-temperature high-power lithium-manganese battery is applied to a temperature environment of -40 DEG C, and the discharge current is greater than 3C. The lithium-manganese battery comprises a positive plate, a negative plate, a ceramic diaphragm, an electrolyte and a battery shell, wherein the positive plate, the ceramic diaphragm, the negative plate and the ceramic diaphragm are sequentially and repeatedly laminated to form a dry cell; the lithium-manganese battery is prepared by putting a dry battery cell into a battery shell, injecting an electrolyte, ageing, sealing and ageing, the positive plate and the negative plate are respectively a graphene-based manganese dioxide positive plate and a lithium-carbon composite negative plate, and positive plate reserved tabs are arranged on the front surface and the back surface of the positive plate; and the front and back surfaces of the negative plate are provided with negative plate reserved tabs. According to the present invention, with the application of the optimal material and the optimal process technology, the beneficial effects are completely explained, the high-power discharge performance of the battery in the ultra-low temperature environment is effectively improved, and the lithium ion battery is suitable for the application in the fields of power consumption type electronic digital, special exploration, starting power supplies, military equipment power supplies and the like.