Abstract: Due to the reflection by collisonless shock, ion beam can be formed in upstream of collisionless shock. In this paper, a one-dimensional hybrid simulation is performed to investigate beam plasma instabilities for two cases:low (n_b/n₀=0.02) and high (n_b/n₀=0.2) beam densities, where n_b and n₀ represents the beam and background plasma density respectively. The results show that for low beam density the beam mainly excites the right-polarized waves through resonance interaction. The waves propagate parallel to the ambient magnetic field, and they can only decelerate a.nd heat the beam protons. When the beam density is high, the beam can excite the waves with propagation direction parallel and anti-parallel to the ambient magnetic field. These waves can interact with beam protons relying on resonance condition, while they interact with background protons due to non-resonant effects. Besides decelerating and heating the beam protons, they can also accelerate and heat the background protons. Their effects on the dissipation of quasi-parallel collisionless shock are also discussed.