Computer simulation provides a useful approach for the studies on the issues related to living bone. Here, we performed two simulation studies on the spongy bone remodeling through Huiskes et al.'s semi-mechanistic bone remodeling theory. In the first study, a 2D finite element (FE) model was developed. The simulation results suggested that decreasing osteocyte density could cause spongy bone loss in healthy old adults, and reduction in osteocyte mechanosensitivity might contribute to excessive bone loss in osteoporotic bones. In the second study, we extended Huiskes et al.'s theory for overloading condition with respect to clinical findings and proposed a 3D FE model. It was the first 3D simulation which showed the spongy bone loss caused by overload. It supported our hypotheses that overload increased osteoclastic activities and reduced osteocyte influence distance. The simulation results in both two studies are in agreement with existing experimental evidences, also with Wolff's Law.