In this paper, we propose a high-sensitivity double-sided polishing photonic crystal fiber biosensor based on surface plasmon resonance. The performance of the sensor was analyzed by finite element method, including the influence of different pore sizes and position, polishing depth, pore spacing, metal thickness, refractive index(RI), and manufacturing error (5%) on the sensing performance. We also analyze the performance of the modified sensor in early cancer detection applications. Our use of a double-sided polishing structure and coating with a gold layer not only increases the contact area between the analyte and gold layer but also provides a large enough space for the analysis channel, which is conducive to the actual manufacture and use. The sensor has a detection range of 1.35-1.39, the maximum wavelength sensitivity of 21500 nm/RIU, the average wavelength sensitivity is 9550 nm/RIU, the amplitude sensitivity of -1057.1756 RIU-1, the maximum resolution is 4.68×10-6, R2 of 0.98265, figure of merit is 250, and the maximum resolution of 4.68×10-6, which can be used in the cancer detection and other biological areas.