This paper studied a new self-mixing interference (SMI) sensing technology based on the measurement of laser diode junction voltage. The SMI signal was obtained by measuring the variation of laser diode junction voltage. Conventional SMI technology usually employs a detection scheme that utilizes the photocurrent from an external or integrated photodiode (PD) to obtain the SMI signal. In this paper, the SMI signal was obtained by measuring the PN junction voltage of a vertical-cavity surface-emitting laser(VCSEL), which simplifies the structure of the SMI system and improves the system reliability. The signal-to-noise ratio of the system were evaluated, and the junction voltage signal of the laser diode was compared with the photocurrent signal of integrated PD, the results were found to be consistent.