Abstract: using the alkaline potassium persulfate digestion ultraviolet spectrophotometric method for determination of total nitrogen in water, examining the factors affect the total nitrogen in the experimental results. Experimental results showed that potassium persulfate reagent selection, configuration of the alkaline potassium persulfate reagent, digestion time, digestion temperature and pressure control, the control of hydrochloric acid to join after the reaction time and so on all can influence the outcome of the determination of total nitrogen.