Due to the blocking of the screen section at the bottom of the tubing, the observed bottom-hole flowing pressure in the production wells of an over-pressured gas field might show an unexpected sudden drop, frequent fluctuations and some inconsistent changes with the flow rates, to mask the true behavior of the production wells. With the universal, everlasting poor quality of the flowing data, the identification of the abnormal data and the restoration of the true behavior are crucial in the well performance analysis. This paper proposes a simplified data diagnosis method based on the theory of the advanced production decline analysis and the PVT property of the over-pressed gas reservoir, to process the well production history data and to identify and filter the abnormal data. Then, the processed production data are analyzed through the type-curve matching to calculate the well and reservoir parameters, including the skin, the permeability, and the initial gas in the place. Based on these parameters, single well analytical models are built to generate the well true production history. In the end, the generated well production history is verified.