The present invention provides a fast charging method and system, a terminal, and a charger. The method includes: sending, by a terminal, instruction information to a charger connected to the terminal, so as to instruct the charger to adjust an output voltage and an output current; and converting, by the terminal, the output voltage of the charger into 1/K times the output voltage, and converting the output current of the charger into K times the output current, so that a charging circuit between two sides of the battery charges the battery with the 1/K times the output voltage and the K times the output current, where K is a conversion coefficient of a conversion unit with a fixed conversion ratio in the terminal and is a constant value, and K is any real number greater than 1. The terminal can be fast charged by implementing the fast charging method provided in the present invention.