UV absorption full spectroscopy with many features such as accurate, reliable, simple, fast and practical is used to measure the nitrate concentration in seawater. UV absorption full spectroscopy is used to test nitrate, bromide, chloride, nitrite, turbidity and their mixed solutions with nitrate at 200~370 nm. The UV absorption spectrums of the substance influencing on seawater nitrate measure is analyzed. Through comparing and analyzing nitrate, the UV absorption spectrum features of nitrate and interfering substances and absorbance changed with wavelength are obtained. The linear fitting curve of nitrate concentration and absorbance show that they have good linear relationship and the accuracy of the experiment is verified. The results show that UV absorption full spectroscopy can be used to measure nitrate in seawater.