Many types of field emitters have been studied up to now to improve the emission current. However, only the ideal parameters are taken into account in some designs. In the fabrication process, the structural parameters of emitters may change. Therefore, it is useful to analyze the parameter sensitivity of the field emitter. This sensitivity should also be included in the defect function of the optimum design. In this article we propose a method to calculate the derivative of the electric field and emission current density versus geometrical parameters of emitter. This derivative can be used to represent the parameter sensitivity of the field emitter. Using this method, the sensitivities of some parameters in the diode and triode emitters are analyzed.