The guard region for a randomly select user is introduced based on the stochastic geometry model. The guard region, through which a frequency reuse criterion is proposed, is calculated based on parameters such as user position, path loss exponents and transmission power. A dynamic frequency reuse scheme based on the guard regions of macrocell users is proposed to mitigate inter-layer interference. A frequency reuse criterion, which changes along with user position adaptively and is derived through stochastic geometry theory, is believed to be the first effort that can be found in the literature.