Flexible membrane fixture is new technology which can adapt to the workpiece shape and size change, such as automobile door-trim parts manufacturing. Due to the use of flexible membrane fixture, significantly reducing manufacturing cost and replacing fixture time. In this paper, the design of the flexible membrane fixture is generated, and the application is showed in a case. Natural rubber sheet used as a flexible membrane. The membrane inflation model generated by ANSYS using Mooney-Rivlin method and its simulation result compared with the experiment result. The door-trim model developed by AUTODESK INVENTOR modelling software. This 3-D geometric model was imported to using ANSYS Workbench 18.2. The Finite element analysis was done after assigning loading and boundary conditions. The applied load considered for this analysis is the pressure applied to the membrane while the door-trim clamped by side clamps. The result shows that Flexible membrane fixture has higher flexibility and fixtured door-trim has smaller deformation value than company requirement. Through comparing the design results, it is found that flexible membrane fixture has higher elastic behaviour.