A fiber bending sensor was proposed based on a homemade multicore optical fiber with seven inner cores where the distance between adjacent cores is about 38.78μm. For a section of bending multicore fiber, mode coupling happens between adjacent cores，which provides a method to achieve bending sensing by measuring the transmission spectrum of the bending multicore fiber. The multicore fiberbased bending sensor is fabricated by splicing a sevencore fiber with a length of approximate 1 m to single mode fibers. When a broadband light is injected into the central core of the multicore fiber on one side, the transmission spectrum with the information of bending curvature can be measured by an optical spectrum analyzer. The relationship between the wavelength shift of the transmission spectrum and the bending radius of the multicore fiberbased bending sensor shows that the output spectrum of multicore fiber under bending condition has much more obvious crosstalk phenomenon along with the bending curvature of multicore fiber increasing.