Abstract: Non-contact detection of internal micro-defects of the micro-electro-mechanical system and minimechanism required a high accuracy and strong penetration test. The current detection methods were difficult to achieve high precision while also having strong penetrating power. In response to the above problems, a composite system of ultrasonic detection and digital holography imaging was designed. Ultrasonic detection technology had strong penetrating power, and digital holographic imaging had higher resolution. The composite system designed included a near-field ultrasonic subsystem, an digital holographic subsystem and a synchronous control subsystem. In the near-field ultrasonic subsystem, the generated near-field ultrasonic wavefields passed through the internal defect of the sample and formed the surface ultrasonic wavefield on the surface of the sample. The digital holographic subsystem mainly measured and analyzed the transient morphology of the surface ultrasonic wavefields, and the internal defect information contained in the surface ultrasonic wavefield could be analyzed. The experimental results show that the system can measure the transient 3D topography of the ultrasonic wavefield by analyzing the ultrasonic wavefield, and can effectively detect internal defects of 50 μm.