Abstract¡G Scalar coupled mode theory predicts that the output powers at two nonlaunch fibers are identical for the equilateral 3x3 fiber couplers due to the geometrical symmetry, but several experimental results demonstrate that they are not equal. In this work, a power coupling model with considering the polarization property of input power is proposed for the equilateral 3x3 fiber couplers. Consistent with the measurement results, the model shows that when a polarized light is launched into one of the three fibers the output powers at the other two nonlaunch fibers are unequal.