A chain of truncated ellipsoid model is proposed to study the magnetization reversal mechanism of the magnetic nanowire in accordance with the real topological structure. Based on this model, the expressions of critical field for the irreversible reversal magnetization and the coercive force are derived for both the parallel rotation and symmetric fanning mechanisms. The influences of the contactangle of the ellipsoids, the uniaxial magnetocrystalline anisotropy, the angle between the applied magnetic field and the axis of the chain, the number of ellipsoids and the shape factor of single ellipsoid on the critical field and the coercive force are discussed. The results based on the model indicate that the magnetization reversal process of the Ni nanowire may have the symmetric fanning mechanism.