Flexible substrates are becoming more important in the printed circuit board industry. The flexible circuit boards can be thinner and lighter than rigid board, and can be flexibly and easily assembled into high level electronic product. In this paper, we developed the ink jet printing technique to form the copper metal wire on flexible substrate. It combines the self-assembled polyelectrolyte as surface treatment, the ink jet printing of catalyst, and electroless plating processes into one continuous roll-to-roll system. Specially, the working surface of the substrate is kept out of contact with each transmitting roller to avoid the pollution in this continuous roll-to-roll circuit fabrication system by ink-jet printing. This design is important for modular process flow. To avoid the elongation and alignment deviation of flexible substrate, this continuous roll-to-roll system also has a robust tension control to guarantee the position accuracy of about ±10μm. In this study, all the process flow are tabulated and discussed, especially in the arbitration between the ink-jet patterning step and other processes.