One of the problems in surface physics which has not been solved for a long time is the atomic structure of reconstructed Si(lll)2×l surface. Basing upon the calculations on dynamics of low energy electron diffraction (LEED), we analysed the intensity-voltage curve in detail to test a lot of proposed models. The buckling π-chain model has been confirmed by our results. The atomic coordinates down to the sixth layer have been further modified, so that the agreement between theoritical calculation and experiment has been improved. The most salient feature of our optimum structure is a buckling of 0.44 ?. Finally, it has been shown that the existence of relaxed 1×1 domain in Si(lll)2×l surface caused a significant effect on the results. The R-factor of integral beam will be reduced considerably by taking into account the existence of relaxed 1×1 domain.