We theoretically investigate the optical absorption coefficient (OAC) of an asymmetric quantum dot (QD) in the presence of an uniform magnetic field. Using the effective-mass approximation, we study the electronic structure of the QD. We obtain the linear, nonlinear and total OAC by the compact-density-matrix approach and iterative method. The results of numerical calculations for the typical GaAs/AlGaAs QD show that the OAC depend strongly on the radius of the QD, parameters of the asymmetric potential, external magnetic field and incident optical intensity. Moreover, the peak of the OAC shifts with the magnetic field or the radius of the QD changing.