Abstract: Aiming at the advantages of grating scale has that it can set reset for power outage, has no cumulative error with high accuracy, we established the unsealed and sealed absolute grating experimental systems respectively by using the technology of image identification on the optical vibration isolation platform.Taking the air bearing linear motor ArotechABL1500 for reference,we checked its accuracy by the laser interferometer RENISHAW XL-80, and analyzed the characters and the causes of the bit errors of different-structure absolute grating scale. By the contrast experiment and the analysis, it is proved that the bit error rate of the sealed absolute ruler is higher than that of unsealed, the bit error rate of the sealed absolute ruler is 3% while the unsealed one is 8%.