Bend due to spanning seriously threatens the safety of subsea pipelines. Quasi-real-time detection of pipeline spanning can be achieved by using spherical detectors ( SDs) with low blockage risk and convenient launch / retrieve procedures. In this paper, via rationally arranging the accelerometer and mass distribution, the fixed-axis rotation of the SD is realized, the accurate output model of the accelerometer is formulated, and the AC component’s frequency and DC component of the recorded acceleration are accurately extracted and then used to indicate the downward bend of the spanning pipeline. By extracting the DC component from the acceleration data through peak detection or continuous wavelet transform, high-sensitivity detection of pipeline bend can be achieved. If the characteristic peak of the acceleration spectrum is a single peak, the pipeline has no bend; if the characteristic peak has a broadening phenomenon, the pipeline has bend. For a 12 m pipe, the bend detection resolution can reach 1 cm.