Composite board defect detecting device based on nonlinear acoustics feature parameter belongs to the composite board defect detecting field. It solved current ultrasonic wave nondestructive test device be difficult to to detect among the composite board small defect or to the problem that the detection precision is not high of small defect. The device comprises computer, ultrasonic signal emergence module, an ultrasonic emission sensor, the 2nd ultrasonic emission sensor, composite board, ultrasonic wave receiving sensor, ultrasonic signal collection module. The utility model discloses the ultrasonic wave that utilizes two kinds of different frequencies detects the small defect of composite board, has utilized when having the defect in composite board the very obvious characteristic of non - linear modulation phenomenon just to regard modulation frequency as the ultrasonic wave nonlinear characteristic parameter that detects small defect among the composite board, make the precision that detects small defect improve greatly. The utility model is suitable for a combined material sheet flaw's detection.