This study investigates the free shape curve and calibration process of piston rings to address the differences between their assembly state and free state in isolation valves.This article adopts static reverse research to obtain the opening size of the piston ring in the free state of the isolation valve，and conducts mechanical tests on its opening size.The results indicate that the opening size meets the requirements of assembly mechanics.Additionally，the formula for the free state curve of the piston ring under isobaric conditions.A calibration method for isolation valve piston rings was proposed， and a reasonable calibration scheme was verified and optimized using finite element static simulation technology.These findings provide a fundamental method for small batch processing of piston rings.