Thin film sensor has the advantages of small size and low cost, which has become a research hotspot in recent years. A measurement system of passive optical fiber DC current sensor based on the thin film sensors is designed in this article. Designs of electric-heating converter, heating-light converter and low-voltage measurement display system are introduced in detail. Experimental results indicate that the general linear correlation between the time constant of fluorescent lifetime and the voltage across the thin film resistor. The feasibility of measurement system is verified via the results of the experiment.