Quasi-one dimensional organic conductor (TMTSF)2X with octahedral anions X = PF6, AsF6, and SbF6 have been studied by NMR measurements at the Se-sites which are substantially responsible for conductivity in this system. Close resemblances in the temperature dependence of the spin-lattice relaxation rate 1/T1 and the evolution of internal field in the SDW state were observed in the three measured compounds. The existence of the sub-phases in the SDW phase of all these compounds, which is evidenced by T1 but not from spectrum measurements, indicates that this is a common feature among (TMTSF)2X system with an incommensurate SDW wave number and is associated with dynamic property rather than static one.