Abstract: Abstract: Reactive mufflers have been widely used for noise attenuation due to their relatively simple structure, low cost, and broadband sound attenuation. Typical examples are pumps and compressors, engine exhausts, building ventilation systems, and so on. An important index for the acoustic performance of muffler is transmission loss. For the reactive muffler, the transmission loss is closely related to its structure parameters, such as radius of inlet or outlet pipe, radius of expansion chamber, location of baffle, and radius of baffle hole. Therefore, the focal point of this paper is to analyze the relationship between structural parameters and transmission loss of mufflers. Firstly, a two-dimensional theoretical model of a dual-chamber reactive muffler was proposed based on the sound wave equations in the muffler. This two-dimensional analytical method that calculates the transmission loss of the two-chamber muffler has 2 advantages. On the one hand, analytical method can calculate higher frequency than transfer matrix method which is limited in cutoff frequency; on the other hand, the calculation speed of analytical method above is faster than traditional finite element method. What was more, the accuracy of the model was verified by transmission loss experiment, which was illustrated in previous paper. Then, based on the theoretical model above, a group of orthogonal test L9 (34) of a dual-chamber muffler was conducted to analyze the effect of the structural parameters on its transmission loss. Test index was the average value of transmission loss in 1 000-3 000 Hz frequency band, in which the noise is relatively difficult to attenuate. The result showed that the primary and secondary order that the reactive muffler structural parameters influenced its transmission loss was radius of expansion chamber, radius of baffle hole, location of baffle, and radius of inlet or outlet pipe. Moreover, a group of optimized parameters of the muffler were determined in the orthogonal test. The transmission loss of optimized muffler significantly was raised in 1 000-2 000 Hz frequency band and the acoustic performance increased by 5.8% compared to the maximum value of the orthogonal test. Then, a uniform design U25 (259) of a dual-chamber muffler was conducted to obtain transmission loss predicting model for a reactive muffler. Test index was the same as the orthogonal test. According to the results of the uniform design, the quadratic polynomial regression equation of transmission loss was derived from regression analysis, which could reflect directly the relationship between transmission loss and structural parameters of a dual-chamber reactive muffler. Comparing the average transmission loss from regression function with the theoretical calculated one, the average error was 2.85%, which showed a good agreement. Furthermore, other 2 groups of structural parameters of a dual-chamber muffler which were different from the uniform design were chosen to verify the transmission loss predicting model. The errors between the regression values and the theoretical values were less than 3%, which showed that the accuracy of the predicting model was acceptable. The optimal solution of the regression equation was solved. Compared to the optimal value of the orthogonal test, the average value of transmission loss of the optimal solution in 1 000-3 000 Hz increased by 19.5%. The study in this paper demonstrates that the transmission loss predicting model of a dual-chamber reactive muffler can be used to predict the transmission loss effectively and efficiently, which is helpful for the analysis and design of the muffler.