The spectral ratio method’s rationality of horizontal to vertical component (H/V method) for microtremors is discussed by an elastic layer over a half-space and probability model. The H/V expressions of body microtremors for layered media are derived. The feasibility of estimating the horizontal transfer function from H/V of microtremors is discussed. It is shown that the spectral ratio method of horizontal to vertical component can be used to estimate the site predominant frequency for body microtremors when the impedance ratio is more than 3. However the amplification factor of this method is smaller compared with site horizontal transfer function.