In this paper a new method of removing trace ammonia (NH

3

and H

4

+

) from high purity water by using electrodeionization(EDI) was studied.The removing of ammonia from high purity water and its mechanism were investigated.The dependence of the effectiveness of removing ammonia (NH

3

and NH

4

+

) on electrical current

inlet conductivity

inlet flow rate and pH value was shown.After one EDI treament the total ammonia concentration was decreased from 208mg/L to 0.072mg/L.This method is also effective for removing NH4+ ion from water.After EDI treatment NH4Cl concentration was decreased from 20~100mg/L to below 0.026mg/L.This method giving ammonia concentr

ation much less than the required concentration of ＜0.5mg/L for space water proved to be the most effective among other methods for removing trace ammonia in high pure water.The species configuration during removing ammonia from water was also investigated.