The invention discloses a continuous ink supply system for a printer. The continuous ink supply system comprises an ink tank, a connecting device and an ink box. The ink tank and the ink box are connected through the connecting device. The ink tank comprises a control system, a weight sensor for sensing the ink volume and a low ink level prompting device. The weight sensor and the low ink level prompting device are connected with the control system. An ink bag for continuous ink supply is placed on the weight sensor inside a drawer, changes of the weight of ink in the ink bag will be monitored by the weight sensor in real time, and the printer is informed through the low ink level prompting device that ink is about to be used up, so that ink is supplied in time. Particularly, the continuous ink supply system can inform the printer to perform the ink supplementing procedure by monitoring changes of the weight of the ink in the ink bag, and the technical problem caused when the sensor is soaked with ink is avoided due to the fact that the weight sensor does not make direct contact with the ink. Meanwhile, the continuous ink supply system is convenient to operate and saves time and labor.