Wireless communication is an emerging field for THz frequency band specially for space,imaging, defence and biomedical applications. In this paper a staircase shaped THz MIMO antenna of size \(54\times 40\times 9 \; \upmu \text {m}^{3}\) for 8.61–9.66 THz operating band is designed on silicon dielectric substrate with Graphene patch. The maximum gain for the proposed design is 7.5 dBi with radiation efficiency 79 \(\%\) . Enevelope correlation coefficient and Channel capacity loss both are less than 0.5 and isolation greater than 10 dB for all over the frequency range. The phase combinations of \(180^{o}\) , \(180^{o}\) and \(120^{o}\) , \(180^{o}\) excitation signals, shows the similarity with the measured \(S_{11}\) parameter. Designed antenna placed in line of sight configuration and results are analysed in the form of S-parameters.