We have developed an in-situ X-ray imaging system to visualize penetration dynamics of small ink droplets into powder bed in binder jetting process. The imaging system consists of a micro focus X-ray source, an ink depositing device by remote control and a high resolution flat panel detector. The whole process of the ink penetration, such as ink penetration through the powder bed and powder bed densification, was visualized in sequence applying this system. The results show that the difference of the amount of ink cause the change of the powder bed densification and the penetration distance in depth and plane direction. The real-time visualization of the ink penetration dynamics can be useful to clarify the mechanism of the defects in the fabricated objects, such as internal porosity and weak bonds between the layers.