The invention relates to an image acquiring device and a method for shifting the charging capacitance of a flashlamp thereof. The image acquiring device comprises a flashlamp charging capacitance shifting device, and the flashlamp charging capacitance shifting device comprises a flashlamp controlling unit, a capacitance charging/discharging unit, a charging capacitance shifting unit and a brightness judging unit. The capacitance charging/discharging unit is coupled with the flashlamp controlling unit and comprises a plurality of capacitors connected in series and a plurality of switches; the charging capacitance shifting unit is used for controlling each switch according to exposure compensation parameters; the brightness judging unit is used for calculating the ambient brightness value of a first image which is acquired in the first state and the preflashing rightness value of a second image which is acquired in the second state, comparing the ambient brightness value and the preflashing rightness value to generate a comparison result, judging whether the comparison result is less than threshold and obtaining the exposure compensation parameters according to the comparison resultand driving the flashlamp controlling unit to flash correspondingly by using the exposure compensation parameters if the comparison result is less than threshold.