The binocular optical axis parallelism of photoelectric instrument is an important indicator.In order to achieve the all-weather quantitative measurement of the binocular optical axis parallelism,the optical axis parallelism digital calibration instrument for binocular photoelectric instrument was designed.To meet the precision demand of the instrument performance parameters,according to the measurement principle,combined with the system components,various factors that affect the measurement precision were analyzed.And a measurement precision comprehensive uncertainty model was established.By analyzing the influence weight of single factor on the comprehensive uncertainty,the methods and measures were put forward to control key error factors.A reasonable error distribution was carried out to optimize the measurement precision of the parallelism calibration instrument.