By using the first principles method based on the density function theory (DFT) and the local density approximation (LDA), we study the ferromagnetic properties in N-doped(1120) ZnO thin films. Magnetic properties in one-N-doped ZnO are investigated. The spontaneous spin polarization comes from N 2p, O 2p and Zn 3d. Magnetic properties in two-N-doped ZnO are also investigated. The calculated results show that ferromagnetism (FM) coupling between N atoms is more energetically favorable for nine geometrically distinct configurations. The origin of the FM state in N-doped ZnO is also discussed by analyzing the coupling of N levels. Finally, the magnetic exchange coefficient and the Curie temperature are discussed. The result indicates that N-doped ZnO thin films show weak FM properties.