The utility model provides a vehicle-mounted lamp constant current driver with an over-current protection function; the vehicle-mounted lamp constant current driver comprises a power supply circuit, a driving circuit, a comparison circuit and a control circuit; the power supply circuit divides the industrial voltage into two groups, wherein one group is used for providing power for the control circuit, and the other group is loaded on two ends of the industrial voltage and used for completely opening a MOSFET on the driving circuit; the control circuit outputs a control signal to the driving circuit so as to control a vehicle lamp to open or close; the control circuit detects a feedback signal outputted by the comparison circuit; if the feedback signal is abnormal, the control circuit can determine the vehicle lamp having short circuit, so the control circuit can generate the control signal to close the driving circuit. The over-current protection vehicle-mounted lamp constant current driver can provide stable current when the vehicle-mounted lamp is in normal work, and can cut the current when the vehicle-mounted lamp is in short circuit, thereby preventing the elements from being burned by overlarge current.