An object detection method based on statistical theory and generalized likelihood ratio tests (GLRT) method is proposed to solve the object detection problem under photon noise limited condition. The object under photon noise limited condition follows Poisson distribution and present particle states. And the signal-to-noise ratio (SNR) of the image is low,so it is hard to detect and identify. Statistical decision formula has been obtained by Poisson distribution probability function and GLRT method under the known grey level image of object. Object detection is determined after the calculation of GLRT value. Simulations and experiments show that the method has good object detection performance,and the results also verify the effectiveness and practicability of the method.