Abstract: By using the method of undetermined coefficients,the author discusses some solutions of the equation ａｘ·（ｔ－τ）＋ｂｘ·（ｔ）＋ｃｘ（ｔ－τ）＋ｄｘ（ｔ）＝ｔｋ.The expressions of the solutions are obtained in the following four special cases:(1)c+d≠0;(2)c+d=0,a+b-cτ≠0;(3)c+d=0,a+b-cτ=0,cτ-2a≠0;(4)c+d=0,a+b-cτ=0,cτ-2a=0.

Key words: Neutral differential difference equation, solution, expression