The invention discloses a boron diffusion method of a crystalline silicon solar cell. The method comprises the following steps of: (1) putting a silicon chip which is felted and cleaned into a diffusion furnace tube, raising temperature to 800 to 1,000 DEG C, filling oxygen, and oxidizing for 1 to 30 min; (2) keeping the temperature in the step (1), or raising the temperature to 900 to 1,100 DEG C, and filling a boron source, the oxygen and nitrogen for boron diffusion; (3) stopping filling the source, keeping the temperature or reducing the temperature to 800 to 900 DEG C, and keeping the temperature for 5 to 50 min in the nitrogen atmosphere; and (4) reducing the temperature, taking out the silicon chip, and finishing the diffusion process. By adoption of the method, the uniformity of the boron diffusion can be improved, formation of a boron-rich layer is avoided or reduced, and the minority carrier lifetime of the silicon chip is prolonged; and meanwhile, high surface impurity concentration can be kept, and high ohmic contact is formed, so the performance of the cell is improved.