Grazing incident X-ray reflection (GIXR) is widely used in film detection and high accuracy characterization because of its high detection accuracy and nondestructive measurement. However, it is a kind of indirect measurement method, and therefore it requires a superior numerical optimization algorithm when solving thin film parameters, especially for complicated multilayers. A new method based on quantum-inspired genetic algorithm (QIGA) is proposed to realize GIXR fitting. The proposed algorithm is applied in fitting the GIXR of Si single layers and periodic Mo/Si multilayers. The results indicate that the algorithm based on QIGA has fast solving speed and high fitting precision, and QIGA has potential values in the field of thin film characterization.