The invention provides a drainage device for accumulated liquid in an annular space. The drainage device comprises a string, a packer, a through hole, a check valve and a pressure device. The string can be tripped into preset positions in a bushing of an oil steam well, the annular space is formed between the string and the bushing, the string is provided with a first end and a second end, the first end of the string is close to a wellhead of the oil steam well when the string is tripped into the bushing, and the second end of the string is far away from the wellhead of the oil steam well when the string is tripped into the bushing; the packer is connected with the string and is positioned between the first end and the second end of the string; the through hole is formed in the wall of the string in a perforated manner and is formed in a position between the first end of the string and the packer ,and the annular space and the string can be communicated with each other via the through hole; the check valve is arranged in the string, and the through hole can be blocked by the check valve, and can be unblocked by the check valve when the internal pressures of the annular space reach preset values, so that the annular space can be communicated with the string; the pressures can be applied to the annular space by the pressure device, and a pressure output opening of the pressure device is communicated with the annular space.