For the problem of detecting oxide inclusion defects in aluminum alloy for spacecraft， the experimental research on ultrasonic detection technology was carried out.An oxide inclusion defect simulation method of aluminum alloy based on interference fit and rapid oxidation principle was used to simulate oxide defects， and the microstructure and composition of defects were analyzed.Analysis results verify the fabrication effectiveness of oxide inclusion defects. Test results show that the mechanical C-scan can distinguish defects under Φ1.2 mm effectively. For inclusion defects of about 1.2 mm equivalent，the detection effect is better than manual scanning in terms of intuition， coupling stability and repeatability.The method has been applied to the detection of oxide inclusions in spacecraft aluminum alloy products with good results.