In this paper, the content related to scattering information is mainly focused in the presence of complex additive Gaussian white noise (CAGWN). In our previous works, the theoretical formula of the scattering information is already derived with integral operation. To get more brief expressions, we derive the approximate expressions in cases where the signal-to-noise ratio (SNR) is high and low separately. Noting that the a posteriori probability density function (PDF) obeys Gaussian distribution in the case of high SNR so it’s natural to derive the expression of the scattering information’s approximate expression on account of information theory. In low SNR regime, an approximate formula can be obtained with the reason of signal is submerged in the noise. Numerical results are presented to verify the effectiveness of the proposed approximation.