The invention relates to a method for diagnosing the crop water deficit through a hyperspectral image technology, and especially relates to a method for diagnosing the Lycopersicon esculentum Mill. leaf area water based on hyperspectral images. The method comprises the following steps: 1, acquiring Lycopersicon esculentum Mill. leaf hyperspectral image data through a self-constructed hyperspectral imaging system; 2, selecting a characteristic wavelength by optimizing through an adaptive band selection process to realize multidimensional datum dimensionality reduction; 3, dividing the image ofeach sample at the characteristic wave, counter-rotating, carrying out form operation to obtain a target image, and extracting the leaf gray level and the leaf texture characteristic from the target image; and 4, selecting an optimal characteristic subclass through a GA-PLS (genetic algorithm-partial least square) process by fusing the gray scale and the texture characteristic and aiming at ten characteristic variables, and establishing a partial least square regression model based on the optimal characteristic, wherein the correlation coefficient R between a predicted value and a measured value of the model is 0.902. Compared with routine detection methods, the method of the invention has the advantages of rapid detection speed, and simple and convenient operation; and compared with a single near infrared spectroscopy or computer vision technical means, the method of the invention allows obtained information to be comprehensive, and the accuracy and the stability of the detection result to be improved.