A process for preparing a secondary battery including a positive plate, including a positive current collector and a positive film arranged on at least one surface of the positive current collector and including a positive active material, the positive active material comprising one or more of layered lithium transition metal oxides and the modified compounds thereof; and a negative plate, including a negative current collector and a negative electrode film arranged on at least one surface of the negative current collector and including a negative active material, the process including preparing the negative active material by taking a non-needle-like petroleum coke as a raw material, smashing the raw material and removing fine powder; placing the raw material into a reacting kettle for heating, shaping, and removing fine powder, so as to obtain an intermediate product 1; graphitizing the intermediate product 1 at a high temperature, so as to obtain an intermediate product 2; and mixing intermediate product 2 in a mixer and then sieving, so as to obtain an artificial graphite A; taking a needle-like green petroleum coke as a raw material, smashing the raw material and removing fine powder; and graphitizing the raw material at high temperature and sieving, so as to obtain an artificial graphite B; mixing the artificial graphite A and the artificial graphite B to obtain an artificial graphite; taking flake graphite as a raw material, smashing and spheroidizing the raw material, so as to obtain an intermediate 1; chemically purifying the intermediate 1 to obtain an intermediate 2; drying the intermediate 2 and mixing it with pitch for carbonization treatment, and then sieving, so as to obtain a natural graphite; and mixing the artificial graphite and the natural graphite to obtain the negative active material, wherein the negative active material comprises the artificial graphite and the natural graphite, and wherein the artificial graphite includes primary particles and secondary particles, and a number percentage S of the secondary particles in the negative active material satisfies: 10% ≤ S ≤ 50%. taking a non-needle-like petroleum coke as a raw material, smashing the raw material and removing fine powder; placing the raw material into a reacting kettle for heating, shaping, and removing fine powder, so as to obtain an intermediate product 1; graphitizing the intermediate product 1 at a high temperature, so as to obtain an intermediate product 2; and mixing intermediate product 2 in a mixer and then sieving, so as to obtain an artificial graphite A; taking a needle-like green petroleum coke as a raw material, smashing the raw material and removing fine powder; and graphitizing the raw material at high temperature and sieving, so as to obtain an artificial graphite B; mixing the artificial graphite A and the artificial graphite B to obtain an artificial graphite; taking flake graphite as a raw material, smashing and spheroidizing the raw material, so as to obtain an intermediate 1; chemically purifying the intermediate 1 to obtain an intermediate 2; drying the intermediate 2 and mixing it with pitch for carbonization treatment, and then sieving, so as to obtain a natural graphite; and mixing the artificial graphite and the natural graphite to obtain the negative active material, wherein the negative active material comprises the artificial graphite and the natural graphite, and wherein the artificial graphite includes primary particles and secondary particles, and a number percentage S of the secondary particles in the negative active material satisfies: 10% ≤ S ≤ 50%.