In order to realize the early and small-scale oil spill detection and warning, surface plasmon resonance (SPR) sensing technology, which was sensitive to small changes in refractive index of external media, was used. A set of small oil spill detection experimental device was designed and built. A GUI interface based on SPR was created to select sensing parameters. A set of software with functions of data acquisition, storage, processing and display was compiled by C++ for data processing and early warning. The theoretical analysis and experimental verification were carried out. SPR data of crude oil samples with refractive index of 1.4451, 1.4774 and 1.5299 were obtained. The results show that the experimental data are in agreement with the simulation results. The device can be used in the experimental study of oil spill detection at sea. Its software design meets the needs of early warning. This result is helpful to the detection of oil spill at sea.