The utility model discloses a constant current power supply with incessant illumination function of LED, including main power circuit, stand -by power supply circuit, switching circuit, control circuit and constant -current source circuit, main power circuit includes isolation transformer, rectification filter circuit and DCDC reduction voltage circuit, and isolation transformer and rectification filter circuit are connected, and rectification filter circuit is connected with the input of DCDC reduction voltage circuit, the output and the switching circuit connection of DCDC reduction voltage circuit, stand -by power supply circuit includes battery, undervoltage protection circuit and boost circuit, and the battery passes through the undervoltage protection circuit to be connected with boost circuit, boost circuit and switching circuit connection, control circuit includes controller, display module, input device, AD converter and DA converter. The utility model discloses a main power source and reserve two way powers make voltage output stabilize at 8V, maximum current 1A, and efficiency reaches more than 90%, through the switching circuit that comprises two MOS switch tubes and switch tube drive circuit, realizes fast -speed active -standby switch.