To study bilateral shear strength of rectangular frame column (RFC) with different stirrup area on two principal axis, 12 rectangular frame columns including 5 columns without stirrup and 7 columns with stirrup were tested. The analytical results indicated that the relationship of shear strength between two principal axes of RFC without stirrup could be approximately described as ellipse, and stirrup stress on two principal axes is independent. The oblique shear strength is less than the resultant force calculated by unilateral shear strength formula offered by Code for Design of Reinforced Concrete Structure. The reason for this is shear strength contributed by concrete is considered iteratively on two axes. Based on truss model and the above conclusion, a reduced coefficient is introduced to calculate the bilateral shear strength offered by concrete and the axial force, and then a formula is proposed to calculate bilateral shear strength of RFC with different stirrup area on two principal axes. Comparison between the calculation and experimental results shows the formula is feasible and safe.