Abstract: To solve the problem of continuous carbon fiber reinforced 3D printing composite (C-CFRP) parts, which have lots of defects such as excessive internal voids and stress concentration, an ultrasonic online controlled printing method based on fused deposition modeling technology was proposed in this paper. Firstly, the tensile properties of C-CFRP wire were studied under ultrasonic vibration, which the amplitude were 0 μm, 10 μm, 20 μm, 30 μm, 40 μm and 50 μm. And, the tensile and bending properties of C-CFRP specimens were discussed under ultrasonic vibration, which the amplitude were 0 μm and 20 μm. Secondly, the cross-sectional morphology of C-CFRP wire was observed through a super depth of field microscope, and the microstructure of the fracture surface of C-CFRP parts was observed using a scanning electron microscope. Finally, the mechanism of melt resin infiltration into the fiber by ultrasonic controlled was analyzed. The results indicate that the mechanical properties of C-CFRP wire were first increased and then decreased with the increase of ultrasonic amplitude value. And the maximum failure load value of C-CFRP wire was 121 N under the amplitude reach 20 μm, which was 16% higher than that in the absence of ultrasound. The tension properties and flexural properties of composite parts were improved by 11% and 23%, under the amplitude was 20 μm, compared to the absence of ultrasound. This article provides a reference for the development of high-performance C-CFRP 3D printing technology.