The laseroptical disdrometer is a new kind of measuring instrument which the Tianjin Weather Modification Office purchased in recent years. It has great influence on the realtime monitoring of precipitation. Based on the laseroptical disdrometer (LPMThies) data, the raindrop spectrum characteristics of a convective precipitation in Tianjin is analyzed. The analysis results show that the variation trend of hourly precipitation between laseroptical disdrometer and tilting rain gauge are well consistent. But the accumulated precipitation detected by the laseroptical disdrometer was heavier. This convective precipitation had large spatial and temporal variation. The rainfall intensity had marked differences between four meteorological stations. The average diameter of precipitation particles was between 040 and 064 mm. Raindrops with the diameters being below 20 mm accounted for more than 95% of the total number of precipitation particles. The fluctuation of rainfall intensity and radar reflectivity was obvious, and raindrop number concentration reached 103 in magnitude basically. The instantaneous spectrums at the three times in Jixian Station presented a unimodal distribution，and the peak value was near 05 mm.