In this study, the underestimation of T2 by TESS was revealed through simulation and phantom study. The bias becomes significant in high resolution TESS imaging with larger unbalanced gradient moment, as the diffusion effect can not be neglected. A possible correction scheme was also proposed, the results validated the diffusion effect on T2 estimation. However, the correction method relies on T1/T2/D as priori to calculate the signal change ratio through EPG algorithm. A possible solution might be simultaneous estimation on apparent diffusion coefficient and T2.