A concave-shaped photonic crystal fiber (PCF) combined with square-channel using indium tin oxide (ITO) for surface plasmon resonance (SPR) sensing is proposed. By means of finite element method (FEM) to multiple parameter optimization of structure, the operation wavelength spans from 1270 nm to 1692 nm covering low-loss communication band when a dynamic refractive index (RI) in a range of 1.19 to 1.29, and meanwhile the sensor displays the maximum wavelength sensitivity of 1700–10700 nm/RIU. This is so far the minimum RI detection sensor in the known reported D-shaped PCF-SPR sensors. It reveals the remarkable ability of our sensor to detect the 10−6 scaled smallest RI changes in solutions of medical oxygen, liquid CO2, and fluorine-containing organics, which extremely expands the application of existing PCF-SPR sensors for medical testing, unknown biomolecules and organic chemistry detections. •The SPR effect is excited by coating indium tin oxide on the rectangle slot.•Detecting the 10−6- 10−5 scaled small RI changes of medical oxygen, liquid CO2 , and fluorine-containing organics.•Low plasmonic material consumption and minute sample detection contribute to high cost-effectiveness.•Uniformly coating film on the flat surface of rectangle open-ring.•Variable side-polished depth of D-shaped fiber make fabrication easier.