A stochastic lattice gas model was formulated to simulate tunnel structure of the Formosan subterranean termite, Coptotermes formosanus, for investigating the effect of food size and distribution and the branch length of termite’s tunnel on foraging efficiency. Based on experiment, minimized local rules governing excavation were executed on the model. In this model, a termite was mimiced by a random walker with transition probabilities from one site to its nearest neighboring site. Food distributions with three types (uniform, random, and clumped) were defined by using I-index proposed by Zimmer and Johnson (1985). In this study, foraging efficiency was defined by counting the number of food removed by workers in search time per lattice site. Foraging efficiency was higher in clumped distribution of foods than in non-clumped (uniform and random) under the condition of the same amount of food. Foraging efficiency was also dependent on food size. In addition, the branch length exponent á determining the length of secondary branch was investigated in foraging efficiency and in cost defined as a total tunnel area. Simulation showed the cross-over representing the economically optimization of branching effect with respect to cost. This result was discussed in relation to empirical data.