The　pressure　induced　twisted　distortion　of　the　diagonal-double　tetrahedrons　(DDTs)　in　Tc2O7　and　the　corresponding　anomalous　lattice　variation　under　pressure　were　unraveled　based　on　van　der　Waals　(vdW)　corrected　density　functional　theory　calculations.　We　show　that　the　optPBE　functional　precisely　represents　the　crystal　structure　of　Tc2O7　with　less　than　0.5%　volume　overestimation.　The　flexibility　of　the　Tc2O7　cell　originating　from　the　weak　vdW　interactions　between　the　Tc2O7　DDTs　is　confirmed.　On　the　contrary,　we　have　found　that　the　strong　ionic　bonding　in　the　Tc2O7　DDT　leads　to　the　rigidity　of　the　Tc2O7　DDT.　According　to　the　analysis　of　chemical　bonding　characterization,　the　pressure　induced　distortion　of　the　Tc2O7　DDT　leads　to　inhomogeneous　Tc-O　bonding　distributions.