A model for estimating flexural strength was proposed in this paper. The model traces destructive mechanisms conscientiously. Therefore it can be applied for the several kinds of glulams that consist of some dimensions, stress conditions and woods. The model means that a lamina of glulam is divided into minute elements in the direction of length and minute elements that have each strength according to knots, finger-joint or clear wood. The element disappears when the element reaches its strength against the applied load. The concentration of stress and progress of cracks can be traced by removing minute elements in this model. The maximum flexural strength of a glulam beam is calculated as the minimum moment among the sums of moments that all elements resist on the same dimension. For confirming agreement of this model, Monte Carlo simulations were carried out. The estimated values using this model agreed well with several experimental data.