The invention relates to a circuit control method for a POS terminal, namely a reliable printing method for a hand-held electric (point-of-sale) POS terminal in a condition of a low battery voltage. The reliable printing method comprises the following steps: comparing and judging a residual voltage value of a battery by a battery voltage comparator in the beginning of printing, when the voltage value is higher than a preset value, performing normal printing; when the voltage value is lower than the preset value, starting a low voltage regulating circuit by a printing circuit; by regulating the speed of a servo motor and synchronously outputting printing data to further realize the reliable and clear data printing in the condition of low battery voltage to prolong the service time of the hand-held POS terminal. By adoption of the method, the service time of the hand-held POS terminal can be prolonged by greater than 20% in the condition of equivalent battery voltage and equivalent capacity without increasing the battery capacity and without adopting an external power supply for direct power supply, therefore, the portability and the usability of the hand-held electric POS terminal equipment are greatly improved.