A directed transport model of coupled Brownian particles in a two-dimensional potential is established. In this model, the system of Brownian particles is driven by biharmonic forces and constant forces. By numerical simulation, the cooperative transport behaviours of the system are investigated. The results show that the average velocity of the system is significantly independent of the frequencies and intensities of the harmonic forces, the barrier height of the ratchet potential, coupling strength and noise intensity. The average velocity increases monotonically with increasing the intensities of the harmonic forces, and can reach some maximum values when the two frequencies are equal. In addition, the average velocity presents stochastic resonance and generalized resonance for noise intensity, coupling strength and the barrier height of the ratchet potential. Moreover, when a constant force is exerted on the ratchet potential direction, it will promote the directed transport of the system. But, when on the non-ratchet potential direction, the transport will not be affected.