The invention relates to the field of UPSs (Uninterrupted Power Supplies), discloses a direct-current output integrated uninterrupted power supply circuit and a control method, and aims to realize an output of zero switching time when an alternating-current input is switched off. The power supply circuit comprises an input end, an output end, an MCU (Microprogrammed Control Unit), a power-off detection module, an AC-DC (Alternating Current-Direct Current) module, a step-up and step-down constant-current charging module, a step-up and step-down inversion module, an auxiliary power supply module and a battery module. The control method comprises the following steps: an output voltage value of the AC-DC module starts to fall from a normal voltage value when no alternating-current signal exists, and the step-up and step-down inversion module switches from a standby state to a working state when the output voltage value of the AC-DC module falls to a set value; energy is supplied to the step-up and step-down inversion module through the battery module, direct current is continuously output to the output end, and meanwhile the MCU controls the step-up and step-down constant-current charging module to keep in a disabled state in order to stop charging the battery module. The direct-current output integrated uninterrupted power supply circuit and the control method are suitable for a UPS.