Studies on runoff-rainfall relationship are important to understand the hydrological processes and the water balance in a small catchment. By the pressure sensor, H-type weir and rainfall collector, the investigation of runoff and precipitation in a small catchment of Taihang mountains were carried out. The relationship between runoff and rainfall are analyzed. The results indicated that the rainfall in the catchment mainly occurred from June to September, in which the volume makes up 86.5%, 389.2 mm of the total precipitation, and only 60.75 mm from November to May. If the rainfall per event is lower than 50mm, the runoff will not be produced and the discharge keeps decreasing. From November 1999 to the end of May, water level of runoff decreased around 15mm, discharge 0.002 3 m 3/s. Saturated soil and heavy rain are the important conditions for runoff-generating, too. Rainfall in raining season usually is too heavy to infiltrate into soil. The surplus water will become surface runoff and discharge out of the catchment. It is heavy precipitation on 4 July,2000, and it causes the soil to saturate, the following heavy event on 5 July, which has a heavy rate of rainfall by 28.91 mm/h, causes a peak flow discharge 0.905 m 3/s after 4 hours. In this period, the linear relationship between discharge and precipitation was given as the following:Q=0.0454P-0.3556,r 2=0.858, p<0.01.However, the peak flow discharge had continued only for 1 or 2 hours. There was not any peak flow although it had a following 57.3 mm of precipitation. It is significant to be used for agriculture and forestry in the lower valley.