The invention discloses a method for realizing a perfectly matched layer through an auxiliary differential equation in plasma. The method comprises the following specific steps: 1, inputting a model file; 2, performing initialization and setting a parameter of the model file in the step 1; 3, calculating an electric field component coefficient E<y><q> by using the parameter in the step 2; 4, calculating an electric field component coefficient E<x><q> by using the parameter in the step 2; 5, calculating a magnetic field component coefficient H<z><q> by using the electric field component coefficients obtained in the step 3 and the step 4; 6, calculating intermediate variable coefficients psi<x><q> and psi<y><q> by using the electric field component coefficients in the step 3 and the step 4; 7, updating and calculating an auxiliary variable of an electromagnetic field component coefficient in a whole computational domain; 8, updating and calculating an electromagnetic field component of an observation point; and 9, assigning q+1 to q, judging whether q is up to a preset value or not, returning the step 3 if q is not up to the preset value, and ending if q is up to the preset value. The method has the advantages of low calculation speed, low memory consumption, and very good absorption effects on low-frequency and evanescent waves.