The invention provides a drying method for a positive electrode material of a lithium ion battery. The method comprises the following steps: a) placing a positive electrode material in a drying chamber with an internal circulation fan; b) vacuumizing the drying chamber; c) introducing a protection gas into the drying chamber; d) heating and vacuumizing the drying chamber, rising the temperature of the drying chamber to a predetermined temperature, and reducing the pressure value of the drying chamber to a predetermined pressure value, wherein the predetermined temperature is 120 to 300 DEG C,and the predetermined pressure value is not more than 20 Torr; e) roasting the positive electrode material under the predetermined pressure value and the predetermined temperature, wherein the internal circulation fan is rotated in the roasting process; and f) cooling and taking out the positive electrode material. According to the drying method provided by the invention, the moisture content of the positive electrode material can be effectively reduced, the total positive electrode material of the positive electrode materials is less than 1400 ppm, and even less than 1000 ppm, the stability for the drying degree of the positive electrode materials can be ensured, and the security and service life of the battery are improved.