The paper resolved a two-dimensional partial differential equation of transverse piezoresistive effect transducers with a method of perturbation.A relationship between the output voltage and device size has been gotten.We also verify that the maximum output voltage is located at middle point of output terminal.An expression of the maximum output voltage has been given.The calculation results based on the expressions are fit to numerical and experimental values of devices.It shows that the analysis model we have gotten is right.These expressions based on the paper can be used in design and simulation of four-terminal piezoresistive pressure transducers.