Abstract: A new technique of adaptive PI controller with specifications on phase and amplitude margins for large dead-time processes is presented.On the basis of process input and output data of normal operation in the control loop,the important frequency responses of process are estimated with signal decomposition and Fourier analysis,and a first-order plus dead-time transform function is identified as well.Finally PI control parameters are calculated to satisfy both phase and amplitude margins.The adaptive procedure of PI controller does not need any prior knowledge of the process while the control loop is still in the normal operation.Simulation examples are given to show both effectiveness and feasibility of the adaptive PI controller for large dead-time process.