How to optimize the absorbing microwave properties by using the parameters of carbon nanotube composite coating is a hotspot in the study of electromagnetic shielding. However, the study on the influence of coating parameters on absorbing microwave properties mainly stays in the stage of experimental study, and the influence of structure parameters of carbon nanotube on absorbing microwave properties has not been reported yet. Therefore, it is significant to study the method of optimizing the absorbing microwave properties of materials through micro-structure of the carbon nanotube composite coating. Based on an equivalent circuit of multi-wall carbon nanotubes, using the relationship between the parameters of each element in the equivalent circuit to study the mechanism of carbon nanotube loss microwave, an expression of absorbing microwave properties about carbon nanotube structure parameters is derived. According to the expression, the microwave reflection ratio of coating is calculated and simulated by Matlab software, which is affected by the length, diameter and coating thickness of carbon nanotube and the number of carbon nanotubes. The simulation result shows that the variation of reflection ratio curve of coating with the number of carbon nanotubes is consistent with the experimental results. The number of carbon nanotubes and the thickness of coating are the vital parameters, which influence the absorption intensity and absorption position, while the diameter and length of carbon nanotube are the vital parameters, which influence the absorption intensity.