To improve the composite precision optical encoder,a large hollow shaft precision shaft was designed using the close packing ball bearing and the close-packing arranging bearing,and errors of the shaft were analyzed.With this method,the radial shaft precision shaft is δ<3 μm,which solves the poor accuracy problem of the large hollow shaft shafting and improves the composite encoder angle measurement accuracy.The experimental results show that the proposed design can meet the composite optical encoder whose accuracy σ <2″.