In this paper

three kinds of measuring instruments（vernier caliper

caliper and projector）are used by different manufacturers to test the external diameter and wall thickness of self-produced optical fiber Loose Tube.Through experiments

it is found that the measuring results of vernier caliper are smaller than those of non-contact instruments（caliper and projector）.The error judgment directly leads to optical cable manufacturers.In the production of Loose Tube

unnecessary raw materials are wasted

which is conducive to the optical cable manufacturing industry to provide a certain scientific basis and reference for the precise testing of Loose Tube.