The invention discloses a star sensor calibration device based on external field star observation and a star observation calibration method thereof. The calibration device comprises a medium-precisionturntable capable of rotating around a zenith, a star sensor arranged on the turntable, and a circuit box connected with the star sensor. The circuit box comprises a data acquisition module and a clock reference module. The calibration method comprises the following steps: step 1, replacing a single-star simulator with starlight, replacing a high-precision turntable with the earth, driving a starsensor through a turntable, simulating a laboratory calibration system, and carrying out a star observation experiment; and step 2, applying a parameter method in laboratory calibration to star observation calibration for data processing; to be specific, constructing an initial alignment error model, compensating an initial alignment error, carrying out nonlinear optimization solution, constructing a distortion correction model, and carrying out least square solution. According to the method provided by the invention, a parameter method in laboratory calibration is applied to star observationcalibration; and especially for a large-field star sensor, the calibration precision is improved.