The invention discloses a rooting method and device. Assisted with control signals from control module, data input device writes the rooting data into data cache module in group and concentrated way on short-term. Rooting module firstly calculates the countdown approximation of data arithmetic root, and uses the hardware resource of reuse iterative part to calculate more precise one, finally multiplies the approximation and the rooting data to complete a calculation with specified precision. Through read analysis of the readable signs from data input device and read capability signs from rooting module, and the read-write operation of data cache module, the control module resolves the influence from rooting module different processing time because of accuracy.