Nd2(Fe1-xMnx)14B crystallize in the tetragonal structure, space group P42/mnm, when xiHc shows a composition dependence. The form of the virgin magnetization curve is characterized by a propagate field Hp. The value of Hp is close to that of iHc, indicating that the intrinsic coercive force is created by domain wall pinning. The temperature dependence of iHc were studied. The strength of the pinning potential barrier was estimated. The Curie temperature and saturation magnetization of Nd2(Fe1-xMnx)14B were measured. The exchange interaction in the pseudoternary compounds decreases dramatically with substitution of Mn for Fe. That results in a decrease of the thickness of domain walls. The magnetization and demagnetization behaviors in Nd2(Fe1-xMnx)14B can be understood in terms of narrow domain walls.