Given the need for flexibility and sensitivity of civil engineering inclination sensors, a dual-core belt inclination optic fiber based on ultra-weak fiber Bragg grating is proposed. Based on the deformation inversion theory of tangent angle recursion algorithm, a flexible inclination model of central wavelength offset is established with respect to optical cable inclination angle. Furthermore, the influence of optical cable structure on the sensitivity of the sensor is analyzed via software simulation. Based on the simulation results, the dual-core belt inclination optic fiber optical cable is prepared and tested. The results show that the inclination accuracy of the optical cable is 182 pm/(°), the maximum relative error of the measured inclination angle is 8.28%, strain transfer efficiency is 88%, and temperature compensation error is less than 4%. The dual-core belt inclinometer optical cable structure overcomes the damage caused by material shrinkage on the optical fiber during thermal processing, reduces the influence of on-site ambient temperature, and exhibits high inclination accuracy. It has a broad application prospect in the field of large scale and high sensitivity flexible survey.