According to the properties of coal-water paste (CWP), a series of experimental nozzles were developed for a detailed study of the effect of nozzle design on CWPs behavior in a pressurized fluidized bed. The particle size and its distribution of atomized CWP using several types of nozzles are measured by PIV instrument and newly developed image processing software, and the effect of a number of factors on the atomizing properties are analyzed. The atomizing experimental results show that the atomization quality of CWP was found by correlating with the characteristics of CWP, gas to CWP mass ratio, atomization air motion, coal particle size distribution and the structure of nozzle etc. Mass median diameter (MMD) of atomized particles decreases with the increase of gas to CWP mass ratio. The proper type of nozzle type and proper parameters for engineering application are suggested. (C) 2004 Elsevier Ltd. All rights reserved.