This paper is aimed at finding the optimum configuration of the number of holes and their arrangement for the 290 _ 140 _ 90 hollow clay bricks with 3-D numerical simulation by a home-made code with finite volume method. Seventy-two kinds of configurations with different hole number and arrays are chosen elaborately and their equivalent thermal conductivities are numerically predicted. In addition, the effects of the hole surface radiation and the indoor-outdoor temperature difference on the equivalent thermal conductivity are also investigated. The major findings are as follows. The radiation of the hole surfaces makes heat transfer enhanced and the equivalent thermal conductivity enlarged in some extent, ranging from 25.8% to 4.6%. The optimum configuration has eight holes in length, four holes in width and one holes in height, whose equivalent thermal conductivity is the lowest and of 0.400 W/(m K),which is only 59% of the highest thermal conductivity of the all cases studied. When the indoor-outdoor temperature difference varies from 50 8C to 20 8C, the equivalent thermal conductivity of the 72 kinds of hollow bricks does not vary too much, usually within _5%. Especially, the equivalent thermal conductivity of the optimum configuration holds no change within this variation range of indoor-outdoor temperature difference