Objective:To evaluate the impression accuracy of different impression methods for flabby ridge.Methods:5 patients with flabby ridge were included.Conventional technique,perforation technique and window opening technique were performed to make im-pressions and then final models were prepared.The optical models of the flabby ridge area were obtained both in patients'mouths and on the master casts by intraoral optical scanner.Data handling and computations were made by using 3D inspection and metrology soft-ware,regarding SD,Mean +and Mean -,with subsequent analysis.Results:The 3D deviation of the models obtained by conventional technique was the biggest,that obtained by window opening technique was the least.Conclusion:Window opening technique can de-crease the deformation of flabby ridge impression.