A quasi-one-dimensional alternating-spin Heisenberg model is used to describe the charge-transfer organic ferromagnet, which is studied by the Green's function method. The magnetic properties of the charge-transfer organic ferromagnet in different temperature regions are obtained. A formula for the critical temperature T c is obtained and is found to be related to the spin of donors, to the intrachain exchange interaction, and to the spatial anisotropy parameter. This conclusion can explain T c of the organic ferromagnet. The spatial anisotropy parameter of the organic ferromagnet [FeCp * 2 ][TCNE] we obtained is consistent with the estimated value of Narayan et al. The Curie-Weiss temperature Θ for the organic ferromagnet [CrCp * 2 ][TCNE] we obtained is Θ = 15.6 K which is near the experimental result of Θ = 22 ± 1 K.