To solve the electromagnetic interference of electrochemical biosensing and improve the sensitivity of optical biosensing, this paper proposes photonic crystal fiber (PCF) sensing structure based on surface plasmon resonance (SRR) and applies to the detection of deoxyribonucleic acid. A thin Au film is coated on the outer layer of the PCF to make direct contact with the solution to be tested. The full vector finite element method combined with an anisotropic perfect matching layer is used to numerically study the structure. The results show that obvious SPR effect is gotten in the refractive index range of 1.333-1.347, and the resonance loss peaks are shifted in the wavelength range of 1300-1400 nm. When the Au film thickness is 60 nm, the duty ratio is 0.6 and the diameter of the air hole is 1.2 μm, the sensitivity of the structure can reach 7250 nm/RIU (RIU is a refractive index unit), the detection limit can reach the order of 10^-6,and the quality factor can be 145 RIU^-1 .