The getting older of people age, the density of bone will be further reduced. The process speed of bone formation decreases progressively after reaching peak bone mass in the age range 25-30 years. The reduction in bone density is known as osteoporosis. This phenomenon occurs due to an interruption on remodelling bone due to some conditions. Therefore, this study is going to simulate the effect of mechanical stimuli on femur bone density using walking and standing mechanical stimuli. In this study, there are four stages passed. First, build the femur bone construction which consists of two layers (cortical and trabecular). Then input the properties of bone based on age (Young’s modulus and Poisson’s ratio). Then calculate the stress, strain and strain rate and calculate the bone density using thermodynamic equation of V. Klika and F. Marsik with Runge-Kutta method of 4th orde. The bone density given standing mechanical stimuli (1290 N) for age 25 is 0.7963 g/cm2 and walking mechanical stimuli (1741.5 N) is 1.0698 g/cm2. Then the bone density given standing mechanical stimuli (1200 N) for age 51 is 0.7703 g/cm2 and walking mechanical stimuli (1620 N) is 0.9885 g/cm2.