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• The transmission loss variation law of exhaust muffler of agricultural single cylinder diesel engine. • Research and analysis on the prominent parameters of muffler transmission loss in its structural design. • Comparative analysis of the influence degree of various structural parameters of muffler on acoustic performance. The TL (transmission loss) is an important index to evaluate muffler performance. The design of muffler should not only consider acoustic performance, but also its volume, manufacturing cost and its influence on comprehensive performance of diesel engine. If the prominent structural parameters of muffler can be found, the TL can be maximized without sacrificing the overall performance of diesel engine and the exhaust noise can be reduced. In this paper, the sound pressure nephogram of muffler at different frequencies is analyzed in depth, and the TL diagram of muffler under various design parameters is calculated by using the AML (Automatic Matched Layer) technique. According to previous studies, the influence laws of several main parameters of muffler, such as F (length to diameter ratio), N (long and short axis ratio) and T (sieve separator perforation rate), on TL are compared and analyzed. The results show that in low-frequency range, the change of each structural parameters of muffler has little effect on TL, while in high-frequency range, the TL changes are obvious. The study found the TL of muffler is most obviously affected by the change of its F, followed by N and T. It provides a theoretical basis for the design of muffler parameters. [ABSTRACT FROM AUTHOR]