An optical fiber curvature sensor based on seven-core fiber (SCF) and polarization-maintaining fiber (PMF) structures is proposed. First, a section of SCF is fused with the PMF, and then a common single-mode optical fiber is fused at both ends as the input fiber and output fiber, respectively. Experiments have studied the curvature characteristics of three sensors with SCF lengths of 80, 100, and 120 mm, respectively. The results show that when the curvature increases, the transmission spectrum of the sensor has a significant red shift, and the curvature measurement can be realized by monitoring the shift of the resonant valley wavelength in the transmission spectrum. The curvature sensitivity of the sensor increases with the increasing SCF length. When the length of SCF is 120 mm, the maximum sensitivity is 17.31 nm/m ^-1. However, the temperature characteristic experiment shows that the sensor with this length has high sensitivity to temperature. Therefore, in order to avoid the influence of temperature on the measurement results, the sensor with the lowest temperature sensitivity and the SCF with a length of 100 mm can be selected for curvature measurement. The maximum curvature sensitivity under this length is 16.79 nm/m ^-1. Compared with other optical fiber structure sensors, the proposed sensor has the advantages of simple fabrication, low cost, and high extinction ratio, which can be used in civil engineering and other fields.