The invention relates to a device and a method for testing the reliability of a grating ruler, and overcomes the problem that present grating ruler reliability test device and detection system cannot simulate actual working condition. The test device consists of a working condition simulating device, a grating ruler installation device and a detection control system; the working condition simulating device comprises a temperature and humidity test chamber, a grating ruler driving system, a vibration loading platform and an oil mist control station; the grating ruler installation device comprises a grating ruler installation platform, an open type grating ruler main ruler, a closed type grating ruler main ruler, an open type grating ruler reading head and a closed type grating ruler reading head; the detection control system comprises a laser interferometer, a grating ruler detection instrument and a control cabinet. The test method comprises the following steps: firstly, inputting performance parameters into industrial personal computer software; secondly, installing a grating ruler to be tested; thirdly, carrying out a test of temperature and humidity simulation loading, vibration loading, power supply voltage change and oil mist for grating ruler reliability influence; fourthly, detecting the precision of the grating ruler to be tested; fifthly, analyzing and recording test data.