Abstract: An analytical method for the determination of 18 trace elements( Cu、Se、and Mn) in blended water retention agent was established using inductively coupled plasma mass spectrometry( ICP- MS). The main component of blended water retention agent is phosphate,which leads to serious mass matrix interference. To eliminate the spectral interferences,the dynamic reaction cell( DRC) mode was used with methane as reactant gas after microwave digestion. The limits of detection were 0.002 ~ 0.084 μg / g,with standard recoveries of these elements were in the range of 82.3% ~ 104.8%. This method was sensitive and accurate for the simultaneous determination of multiple elements.