For accelerating the response and enhancing the sensitivity simultaneously, a novel fluidic sensor based on a side-opened and suspended dual-core fiber and dual-beam interference detection mechanism is first explored and analyzed here. The side opening ensures a fast response by allowing fluidic analyte to approach the fiber core laterally. The dual-beam Mach-Zehnder interferemetry provides a relative higher sensitivity. Calculation results show that a sensitivity of 2.1×10(-6) refractive index unit (RIU) within a response time of 10 s could be achievable, which reflects its potential impact on constructing a fluid refractometer for fast-response and high-sensitivity detection. Moreover, the relationship of the sensing sensitivity and the detected dynamic range of this suspended dual-core fiber structure, polarization, and the transmitting waveband are also analyzed.