We have derived the hyperpolarizability of a chiral molecule from the model of coupled two-oscillators in second-harmonic generation. We gave the susecptibility of a thin film. We discussed the influence of microscopic parameters of a molecule on the efficiency of second-harmonic generation through the relationship of hyperpolarizabilities and susceptibilities. We also have simulated the spectrum of rotational angle of polarization state. Our theoretical results fit the known experimental facts.