We propose and demonstrate a highly sensitive optical fiber sensor for vibration and twist based on a polarization-sensitive effect of mode selective coupler (MSC). MSC is prepared by melt coupling. Based on the polarization sensitivity, high sensitivity testing of twist and vibration is realized. The proposed MSC can be used for twist sensing with different demodulation methods at the same time, including intensity of spectra and modes. The twist sensitivity is –10.383 a.u./deg ( ∼ −0.02 dB / deg). For vibration sensing, the MSC achieves ultrabroadband sensing frequency response span from infrasound (Hz) to ultrasound (MHz) with good fidelity and high linearity of ≈ 1. The signal-to-noise ratio of single- and dual-frequency vibration detection is as high as ∼108 dB. In addition, the MSC can realize the detection of damped vibration signals steadily. The twist and vibration sensor based on MSC have the advantages of high sensitivity, wide frequency response range, good linearity, high stability, high fidelity, and compact structure. It has potential application prospects in the fields of oil field leakage detection, coal mine, and other structural safety monitoring.