Research purposes:In consideration of CPⅢ network and accuracy required for observed values, the simulated calculation on necessary positional accuracy of CPⅢ network and improved CPⅡI net form was performed.

The CPⅢ plane network has the characteristics of high precision as well as large amounts of field observation data.

Combining with practical project,the paper introduces application of CPⅢ net in construction of CRTSⅠ two piece track free orbit,it pays much attention to layout of the CPⅢ net and it\'s application in coarse adjustment and tight alignment of orbit,so as to make sure the exact control of CPⅢ net,it aims to assure successful construction of the track free orbit bed.