Bayesian reconstruction or maximum a posteriori (MAP) method has its superiority over others with regard to image quality and convergence. In this paper, a MRF quadratic hybrid prior, which combines the two priors quadratic membrane (QM) prior and quadratic plate (QP) prior, is proposed. A threshold estimation method based on statistical classification is devised to facilitate a selectively utilization of QM prior, QP prior in the quadratic hybrid prior. Application of the proposed QHM prior in emission reconstruction with joint estimation algorithm is also given. Visional and quantitative comparisons of the results of experiments prove the new proposed hybrid prior's good performance in lowering noise effect and preserving edges.