In view of the study on swelling deformation analysis method of protected seam during the mining process of protective seam, the analysis method of “four invariant points around area” is put forward for the first time. The method determines the swelling deformation of protected seam and analyzes it from the perspective of plane by analyzing the variability of “four invariant points around area” of protected seam before and after the mining of protective seam. Monitoring scheme and area analysis and calculation method are respectively designed applied in coal mine and laboratory; the monitor of “four invariant points around area” has been realized in the mining practice by arranging two measuring lines in the roof and floor of protected seam. The study scheme is designed to analyze the swelling deformation of the protected seam by the application of “four invariant points around area” in the engineering practice; the theoretical calculation method of irregular “four invariant points around area” after swelling deformation of the protected seam is put forward under laboratory conditions based on the Freeman boundary encode vector and measuring the length of quadrilateral side directly with the vernier caliper.; the reasonable scale of the "four invariant points around area" is discussed, it is suggested that different “four invariant points around area” should be established with different scale of 1 times, 1/2 times, 1/4 times and 1/8 times thickness of coal seam. The study shows that the method of “four invariant points around area” of swelling deformation is more accurate than the analysis method of “two fixed-point”; the more cells are divided at 1 times of the thickness of coal seam, the higher the accuracy of calculation is.