Since the resolution of the radar rain data used in the former published rainfall spatial correlation researches was about 1km, and this could not exhibit the rain variation within the small scales less than 1 km, so the high resolution data was needed and was applied to this work. We conducted rain cloud observations with a high resolution of 125m in the summer of 2000 using a 3cm-meteorological radar, and obtained the high resolution reflectivity data from rainfall fields in three rainfall systems. Using these data, average reflectivity, strength of nonuniformity described by an excursion (the difference between maximum and minimum) of reflectivity herein, were calculated at the different spatial resolutions of 0.5km, 1km, 2km, 3km and 4km. The calculation results indicate that the nonuniformity is significant, even within 1km size, the excursion above 10dB is common. Then rainfall spatial correlation function was calculated using high resolution data and the simulated 1 km (low) resolution data respectively, which showed how small scale rainfall variability affects rainfall spatial correlation.