By using raindrop spectrum data derived from DSG5 precipitation meter and ground hourly precipitation data, the characteristics of raindrop spectrum distribution and its relationship to Z-I on a summer typical precipitation process that occurred in Lhasa on July 8-9, 2018, are analyzed. The results show that the trend of hourly precipitation measured by DSG5 precipitation meter and tilting rain gauge is well consistent. The main contributor to the convective cloud precipitation is the raindrops of 2.0 to 3.0 mm, and that of mixed cloud precipitation is the raindrops of 1.0 to 2.0 mm. The concentration of the raindrop spectrum on the mixed cloud precipitation is one magnitude larger than that of the convective cloud. Whether the mixed cloud or the convective cloud, the rain intensity is closely related to the mass-weighted average diameter and number concentration of the raindrops. The raindrop spectrum of this precipitation is well accorded with the Γ distribution. Compared with other areas in the Qinghai-Tibet Plateau, the differences in the spectrum parameters indicate the spatial and temporal differences in the raindrop spectrum distribution. The trends of N₀、μ and λ are opposite to the trend of rain intensity. The parameters of the Z-I relationship of mixed cloud precipitation are less than those of convective clouds. Using the standard Z-I relationship radar may underestimate the rain intensity of convective cloud precipitation in the plateau areas. When rain intensity is less than 2.3 mm·h^-1, radar may underestimate that of mixed cloud precipitation. Otherwise, radar may overestimate precipitation.