Diffuse Optical Tomography (DOT) is a functional medical imaging modality which can determine the spatial optical parameters' distributions inside a medium. The forward model of DOT is described by the diffusion approximation of radiative transform equation (RTE) while the DOT is to recover optical parameters of a medium from the boundary measurements induced by external near-infared (NIR) light. In this paper, we propose a mathematic model of DOT and then give a novel iterative reconstruction method of the proposed model. The new iterative reconstruction method is based on the assumption that the measurement noise is Poissonian while previous iterative reconstruction methods are mostly base on the assumption that the measurement noise is Gaussian, and are of least-squares type. The proposed algorithm is a variant of the well-known EM algorithm. It can also be used to deal with the incomplete boundary measurements. The performance of the reconstruction algorithm including spatial resolution and contrast are investigated with 2-dimensional numerical experiments.