Abstract: Ultrasonic flowmeters serve as essential metering devices for long-distance natural gas pipelines, with a typical upstream installation length of 30D (where D is the nominal diameter). To address varying measurement results under different installation conditions without altering the total installation length, two configurations were compared: "10D straight pipeline segment + plate-type flow straightener + 20D straight pipeline segment + ultrasonic flowmeter + 10D straight pipeline segment" and "20D straight pipeline segment + plate-type flow straightener + 10D straight pipeline segment + ultrasonic flowmeter + 10D straight pipeline segment". Through theoretical analysis, Computational Fluid Dynamics (CFD) simulations, and validation with actual flow test data, it was determined that the first configuration more closely approximated the "fully developed" ideal flow regime, offering enhanced flow measurement stability and adaptability to complex conditions. This study provides an optimized installation solution for ultrasonic flowmeters in practical applications.