The invention discloses a water drain device for low-pressure heaters. The water drain device for the low-pressure heaters comprises the first low-pressure heater and the second low-pressure heater which are connected through an upper low-pressure water drain pipe. The second low-pressure heater is connected with the first low-pressure heater further through a main condensed water pipeline. The main condensed water pipeline is provided with an ejecting and gathering device. The first low-pressure heater is connected with the ejecting and gathering device through a low-pressure water drain pipeline which is provided with a valve. The low-pressure water drain pipeline is provided with a low-pressure drain pump. The first low-pressure heater and the second low-pressure heater are connected with a low-pressure pressurized heater steam inlet pipe. Main condensed water is water of a high quality while water drained from a low-pressure heater is high-quality water cooled by the heater; and the first low-pressure heater and the second low-pressure heater are power plant low-pressure heaters. The water drain device for the low-pressure heaters has the advantages of being simple in structure, flexible in adjustment and low in investment cost, saving energy, avoiding consumption of auxiliary steam and addition of auxiliary power consumption, reducing the operation maintenance cost and overhauling cost and reducing consumption.