Abstract: Some new considerations and developments of the performance diagram of trays (PDT)were briefly described.Some new ideas of constructing PDT were put forward in which the operating limitations were based on hydraulic limitations and mass transfer restrictions. The former was a necessary condition for normal hydraulic operations inside distillation column，and the latter belonged to a sufficient condition for high mass transfer efficiency guaranteed. Thus, the effects of various limitations or restrictions of trays on the distillation column operations could be clearly defined and reliably determined.The method of the feasible & stable range(FSR) was presented for the case of frequent variations of feed conditions.The suitable X/Y coordinates of the PDT were also discussed.