It is difficult to recognize a target object from foggy images. Aiming at solving this problem, a new algorithm is thereby proposed. Fog concentration estimation is the prerequisite for image defogging. Due to the uncertainty of fog distribution, a fog concentration estimation model is accordingly proposed. Establish the brightness and gradient model in the spatial domain, and establish the FFT model in the frequency domain. Also, a multiple branch network framework is established to realize the qualitative estimation of the fog concentration in images based on comprehensive analysis from spatial and frequency domain levels. In the aspect of foggy image target recognition, a residual network is introduced based on Fast RCNN network structure. The fog concentration information is added into the target recognition function to realize accurate recognition of target from foggy images. Experimental results show that the accuracy of AOM is higher than 81 under different fog concentration indoors and outdoors.