The relation between bending loss and curvature radius of the directly curved polysiloxane multimode optical waveguide for optical interconnection is analyzed. The bending loss is computed by using the Marcuse straight waveguide approximation method. The theoretical analysis indicates that the bending loss increases with the order of the mode and decrease-with the radius; the total bending loss transmitting in waveguide exhibits step changes. When the radius is larger than 4 mm, the bending loss is less than 1 dB/cm. The transmitting optical field is simulated by using the BeamPROP software under three different radius 5 mm, 10 mm and 20 mm, respectively. The bending loss is also measured by using digital scattering method. Experimental results indicate that the optical bending loss is between 0.55~0.8 dB/cm when curvature radius is between 5~6 mm, which agree with the theory in view of inherent propagation loss of the prepared polysiloxane straight waveguide.