The selective fabrication of highly ordered nanowires with high aspect ratios was of low reproducibility, which remains a challenge for laboratory research. In this paper, we report a novel approach for selective fabrication of conductive nanowires on a solid surface via diffusion mixing reaction system formed by a chemical pen. The nanoscale-mixing region was achieved by appropriately adjusting the viscosity of the solution and other parameters with the aid of dyes functioned as a flow boundary indicator. Finite element simulations and analysis were performed to understand the generation of mixing regions and guide the improvement of the chemical pen design. Under the optimal parameters, high aspect ratio silver nanowires (aspect ratio ≈ 1800) were obtained. Silver nanowire arrays with uniform width, gradient width and complex patterns were successfully fabricated. The theoretical value of the temperature coefficient of resistance (TCR) for silver was 0.0038 Ω/°C. A single silver wire temperature sensor with 7-fold increase in temperature coefficient resistance (0.0261 Ω/°C) was fabricated to show the advantages of the chemical pen in the fabrication of nanosensors. With the freedom of the region, simple operability and applicability, the chemical pen was expected to a potential and advanced method for selective nanomodification and processing on subcellular interfaces.