Abstract: Spectral information change rule of hydroponic tomato leaves under different fertilization kalium level was explored.Prediction model of fertilization kalium content was established based on spectral information of hydroponic tomato leaves.Results showed that it was complicated that spectral information of hydroponic tomato leaves within 350～2 500 nm range.Reflectivity of hydroponic tomato leaves under high and low kalium level was lower than normal in visible light waves（469～743 nm）and in near infrared waves（743～1 392 nm and 1 500～1 785 nm）.Reflectivity of hydroponic tomato leaves was increasing with the amount of fertilization kalium content going up in the wave of 1 450 nm.