According to the characteristics of the NO

x

sensor probe

the hardware control circuit is designed by using common components

and the STM32F103 is used as implementation platform of control algorithm. The design of the NO

x

sensor special controller based on the reference current control method is developed. The test results show that the designed special controller can accurately measure NO

x

gas concentration in range of（100～1 000） × 10

-6

and the measurement error is controlled within 4. 2 %

which improves the measurement precision compared with the traditional constant voltage control method.