We study the crossover between the BCS (Bardeen, Cooper, Schrieffer) and BEC (Bose-Einstein Condensate) superfluid states in a multi-band boson-fermion model at zero temperature. We consider an attractive interaction between different fermion states and a hybridization between them. The bosons are composed of tightly bound fermion pairs that coexist and interact with the single fermions, via an isotropic boson-fermion coupling g. At zero temperature, where all bosons are condensed, the model has a superconducting phase characterized by a finite composite order parameter, Δab=Δab-gφ, where Δab and φ are the BCS and BEC order parameters, respectively. The zero temperature phase diagram in terms of Δab and φ is obtained as function of the attractive inter-site interaction, the hybridization, the boson-fermion coupling and the threshold energy for forming a pair of tightly bound fermions. We also discuss the zero temperature BCS-BEC crossover driven by changing the attractive interaction, the boson-fermion coupling strength, and the threshold energy. Our results should be relevant for high temperature superconductors and cold atom systems.