It briefly introduced purpose and classification of drill collar ,testing requirments for drill collar in API and petroleum industry standard , as well as the common problems in UT detection .It analyzed effect factors from several aspects ,such ad couplant ,accuracy of calibrating manual hole in UT specimen , selecting K value of UT head ,radius of curvature and abrasion of UT head ,maching mode of drill collar deep hole ,hydrocele or oil in the inside surface of drill collar ,scanning direction and speed in testing ,and so on .It putt forward attentions during UT course