For the purpose of utilizing the waste of bark as sound absorbing material, sound absorption properties and an estimation method of normal incidence absorption coefficient were investigated for the bark fiber on the assumption that the bark was crashed and compressed at a constant bulk density. First of all, the misfits appeared between calculated values and measured values after estimating by using the existing absorption model for fibrous material. Therefore, the approximation method of Delany-Bazley model was applied to the characteristic impedance and the propagation constant that were measured by the two-thickness method for reflecting measured values to the estimation formula. Next, another estimate formula, that could calculate the flow resistivity from the bulk density, was given from the relationship between the both measured values. Eventually, the most suitable compressing condition, that the bark fiber could behave good performance, was identified from simulations by using those optimized estimation formulas for the bark fiber.