According to the stress symbol convention and the order of the main stress， the corresponding Moor-Coulomb yield criteria main stress expression，stress invariant expression，and plastic flow shear angle parameter expression are derived.The correlation between the principal stress expression，the stress invariant expression，the plastic flow shear angle parameter expression and the stress symbol convention and the order of the principal stress size are revealed.It provides the criterion for the reasonable selection of Moor-Coulomb yield criterion expression and shear angle parameter expression.