In order to evaluate the leveling performance of the paddy field leveling machine, the inclination of the harrow was measured using two SensComp 600 ultrasonic sensors. The ultrasonic sensors were fixed on the harrow's end, and distances of each harrow's end to referenced horizontal were measured to calculate the gradient angle of the harrow. Some factors having effect on the measurement of the gradient angle were analyzed, such as the distance measured by the ultrasonic sensors, the measuring angles of the sensor, and the movement of the sensors. Then the angle was compared with the data from an attitude-heading reference system AHRS500GA-226 device. The results showed that the calculated inclination was quite accurate. The maximum static-error and the maximum dynamic-error were 0.08° and 1.00° respectively. Finally, estimating experiments were conducted in a laboratory. Based on the evaluation results, it was concluded that the leveling control system could measure the inclination real-time and exactly, and the whole leveling system works reliably.