A new identification method using the second order plus time delay model for the automatic tuning of the PID controller and a simple and explicit tuning method are proposed, We present a relay feedback test combined with a P controller to identify the process using the second order plus time delay model, Thus, the difficulty to determine the initial proportional gain is overcome. Since the proposed identification method uses the second order plus time delay model to identify the prodess, it can incorporate more various processes such as underdamped and high order processes than the identification method using the first order plus time delay model, In addition, a simple and explicit tuning relation for the second order plus time delay model is proposed in this paper. This tuning relation shows almost the same performance as the optimal tuning parameters, The proposed method needs no numerical technique and shows good performances in both simulation and experimental study.