The structure of chemical sensor has great influence on the performance of the sensor. This article presents an optimum design method to improve dynamic stiffness of the sensor structure. The original resonance frequency and modes shape of the structure are obtained by the finite element analysis. Then a series of reasonable parameters are determined by optimum calculation. In the end, the result of the random vibration analysis verifies that the performance of chemical sensor structure for food hazard detection is improved greatly by the presented method here.