The grating mosaic technique is an effective method to obtain the large-aperture grating of the petawatt laser system. The five degree of freedom parallel mosaic mechanism is designed. The macro/micro dual-drive technique of ball screw and piezoelectric ceramic achieves the location precision of nanometer level in the work range of millimeter level. Based on finite element method, the displacement coupling properties analysis shows that the mechanism has high linearity and the error of displacement coupling is nanometer level. The relative angle deviation of grating mosaic mechanism is less than 0.2 μrad. The displacement deviation is less than 20 nm. Two gratings with size of 200 mm×400 mm are installed in the proposed mosaic mechanism in order to conduct experimental study. The clear image of far-field focal spot is obtained, which proves that the proposed mechanism can meet the accuracy requirement of large-aperture mosaic grating system.