A surface plasmon resonance (SPR) based sensor founded on Photonic crystal fiber (PCF) is suggested and numerically analyzed in the manuscript. The refractive index (RI) detecting SPR based sensor has the ability to identify the analyte range from 1.33 to 1.4. Pure silica is used as a base material and it has high RI value than the analyte RI. Furthermore, an analyte layer and chemically stable gold (Au) layer are also placed at the sensor design. The simulations are done based on the Finite Element Method (FEM). Here, the scaled-down approach has the necessity to increase phase matching point within the core mode and surface plasmon polariton (SPP) mode which tends to the sensor to reach high sensitivity response. At the intersect point of core and SPP mode, the loss curve shows a maximum peak value. The suggested sensor shows the highest wavelength sensitivity (WS) response of 35,943.22 nm/RIU, amplitude sensitivity (AS) response of 2321.36 RIU−1, sensor resolution of 9.04×10−6 RIU, and Figure of merit (FOM) value of 600. It is noted that all the optical parameters show better performance analysis. Furthermore, an external sensing approach provides more fabrication feasibility which marks the offered sensor more suitable for practical experimentation. Besides, the investigated sensor provides the maximum and rapid sensing performance that will be helpful for microfluidic analyte detection, detection of biomolecules, medical diagnostics, virus detection, security, and bio-imaging.