Abstract: The unsealed field cage is widely used in a variety of gas detectors for measuring particle energy and position. The electric field in the field cage is mainly affected by three factors: the strong electric field outside of the field cage, the electrode layout of the field cage, and the periodic structure damage of the field cage. The scope and degree of influence of different factors are different. One or more of the above factors can be affected by changing the distance between the field cage electrode and the detector shell, the pitch of electrode, the electrode width, the electrode thickness, increasing the half electrode structure, local mirror electrode, etc. In this paper, by using the method of control variables, finite element software COMSOL was used to calculate the electric field distribution in different cage structures, and the influence of each parameter on the electric field and its limitations were evaluated. The field cage electric field data was imported into the Garfield++ software to simulate the electronic transport process in the cage and verify the effect of the cage. And the principles for selecting each parameter were summarized to provide optimization guidance for the design of detector field cage in different experiments.