Abstract: Aiming at the challenges of poor sampling accuracy, unstable reagent test results, and excessive carryover contamination in high-speed biochemical analyzers, this study systematically investigates the structural design methodology of sampling needles, using Company A's Project B as a case study. The design focuses on precise adjustment of needle core dimensions, the application of variable-diameter structures, and strict control of the inner and outer wall roughness of the needle core. Reynolds number calculations and ANSYS simulations were employed to ensure optimal fluid dynamics and needle strength, resulting in the successful development of a sampling needle structure compatible with high-speed instruments. Roughness measurements were conducted on sampling needles from different manufacturers, followed by tests on small-volume quantification, reagent performance, and carryover contamination. The results were analyzed in depth based on varying roughness levels. The research demonstrates that needle core dimensions and variable-diameter structures significantly influence fluid dynamics during sampling and needle strength. The optimized needle structure notably improves sampling stability and precision, enhances cleaning efficiency, and reduces residual liquid adhesion. Furthermore, the scientific calibration of parameters such as inner and outer wall roughness is identified as a critical factor determining the overall performance of biochemical analyzers, including quantification accuracy, reagent test reliability, and carryover contamination levels.