Abstract Resolution Band Width (RBW) represents the 3 dB bandwidth of the internal IF filter of the spectrum analyzer, the setting of which greatly affects the clarity of the output spectrum line of the spectrum analyzer. Its reasonable value is essential to correctly distinguish the signals of different frequencies, especially in the case of aliasing of the output spectrum. Thus, it is of great significance to study the relationship between the setting of RBW and the output spectrum. Due to the expensive spectrum analyzer, the RBW adjustment range, frequency range and output accuracy are limited, so this paper will apply an economic, RBW arbitrary adjustable, high accuracy equivalent convolution method for the simulation of the RBW parameters of the spectrum analyzer, and evaluate the effect of RBW and filter type on the degree of output spectrum aliasing based on a typical equal-amplitude two-tone signal input, and finally give setting suggestions on RBW and filter type.