Trihydroxymethylaminomethane (TAM) is a new crystal analyzer with both chemical stability and X-ray analytical performance better than pentaerythrite(PET). The X-ray topographic experiment results show that there are not only a variety of dislocations with Burgers vectors b=±100, ±010, ±001, ±101, ±101 and ± 011 etc, but also macroscopic inclusion arrays or isolate inclusions. The planar defect parallel to (001) plane is occured rarely. Origins of defective formation are discussed briefly.