The　principle　of　effective　stress　is　the　key　stone　of　soil　mechanics,　which　becomes　the　fundamental　difference　between　soil　mechanics　and　solid　mechanics.　As　it　is　put　forward,　the　principle　of　effective　stress　is　always　in　the　debate,　and　the　discussion　focus　is　its　approximation.　From　the　analysis　of　the　assignment　of　the　principle　of　effective　stress,　the　connotation　of　the　principle　of　effective　stress　is　illustrated　as　the　general　rule　between　the　measurable　effects　and　external　loads.　The　effective　stress　establishes　a　connecting　bond　on　the　external　loads　and　the　measurable　effects　such　as　strength　or　deformation,　which　is　defined　as　the　stress　that　can　influence　the　measurable　effects　such　as　strength　or　deformation　directly.　Therefore,　the　effective　stress　is　not　unique,　which　is　the　nominal　term　of　real　stress　and　can　be　given　according　to　the　equilibrium　of　forces　and　the　interaction　of　soil　particles.　The　different　formulas　correspond　to　different　definitions　of　the　effective　stress,　which　explains　the　approximation　of　Terzaghi　principle　of　effective　stress.　Then,　the　physical　meanings　of　the　effective　stress　related　to　the　strength　and　the　deformation　are　given　respectively,　indicating　the　general　law　of　effective　stress-strength　or　effective　stress-deformation.　Based　on　the　Mohr-Coulomb　strength　theory,　the　relationship　between　the　effective　stress　related　to　strength　and　the　shear　strength　is　established.　©　2018,　Editorial　Office　of　Chinese　Journal　of　Geotechnical　Engineering.　All　right　reserved.