In order to effectively prevent and control the serious impact of the oil spill incident on the economy and the marine environment, and aiming at the detection of small area oil spills which were not easily detected in the early stage, an original minitype offshore oil spill monitoring system combined with the characteristics of Surface Plasmon Resonance(SPR) sensing technology, such as instantaneity, high sensitivity and low sample consumption was proposed. Specifically, the optimal parameters and relative fixed positions of the components in the sensing device were determined by simulating with MATLAB on the basis of an adoptive four-layer Kretschmann prism-coupled sensing structure in a non-scanning angle modulation mode and the range of refractive index of crude oil samples. The theoretical detection sensitivity was 6.094×10-5 RIU(Unit: Refractive Index). Under the guidance of the simulation results, an experimental device was set up and the experimental analysis for sucrose solutions and crude oil samples was conducted. The experimental results show that the detection sensitivity of sucrose solution is the same as theoretical simulation sensitivity, which corresponded to 9.017×10-5 RIU. The experimental device is effective, and the crude oil detection result conformed to the SPR response trend. The feasibility of the system solution is verified.