With the development of fiber-to-the-home (FTTH) network, bend-insensitive fiber (BIF) has attracted more and more attention. We focus on bending losses of the trench-assisted bend-insensitive optical fiber. For the trench-assisted bend-insensitive fiber, the refractive index difference of trench, the width of trench and the distance between the core and trench are three important parameters which could influence the bending loss. Combining the three parameters, we investigate the impact of fiber radius and refractive index of the coating layer on the bending losses. It is shown that: bending losses can be effectively reduced by changing the radius of the fiber; with refractive index of the coating layer increasing, the bending losses of the fiber could be effectively reduced for certain bending radius. The conclusion is of significance for designing and manufacturing of bend-insensitive fibers.