A model of low-frequency quasi-periodic oscillations (LFQPOs) of black hole X-ray binaries (BHXBs) is proposed based on the perturbed magnetohydrodynamic equations of an accretion disk.It turns out that the LFQPO frequencies of some BHXBs can be fitted by the frequencies of the toroidal Alfvén wave oscillation corresponding to the maximal radiation flux.In addition,the positive correlation of the LFQPO frequencies with the radiation flux from an accretion disk is well interpreted.