A quantum key distribution protocol with traditional Bob has been proposed recently by Boyer et al. using single-particle state. In this paper, a semi-quantum key distribution protocol is described, in which Einstein-Podolsky-Rosen (EPR) pairs of particles are utilized to generate a secret key in remote places. This extends the quantum key distribution protocol with traditional Bob where the single-qubit channel is replaced by the entangled EPR-pair channel. And quantum Alice is able to do any quantum operations, preparing quantum states and performing quantum measurement, but traditional Bob is not able to prepare and measure a particle in the computational basis, reflect the particles. Furthermore, entanglement states are used in our protocol. The analysis shows that our protocol is secure, which can avoid the beam splitter attack automatically, and the proposed protocol is more efficient than Boyers scheme.