The mass fraction of sulfur contained in the catalytic diesel was determined by microcoulometry measurement, the effects of the integral resistance and magnification to the measurement results were investigated, and in addition, the optimal conditions were confirmed. Under the optimized conditions，precision and recovery rate of the external standard samples on catalytic diesel were investigated, and showed that the sulfur content measured with pretty good accuracy and repeatability with a magnification of 200 times, integral resistance of 600 Ω. It was a simple, rapid and accurate method for measuring large quantities of samples.