Abstract: A method for the determination of total nitrogen in surface water by cadmium-coper reduction method with sample digestion in oven was proposed. Linear relationship between values of absorbance and concentration of nitrogen was obtained in the range of 7.637×10-4-1.375×10-2mmol·L-1, with detection limit (3S/N) of 6.704× 10-5mmol·L-1. The proposed method was applied to the determination of total nitrogen in samples of artificial sea water, running water, sea water and lake water; test for recovery was made by standard addition method, giving values of recovery and RSD′s (n=6) in the ranges of 96.7%-101.3% and 3.7%-3.9% respectively.