The sedimentation of circular particles in a vertical channel filled with Oldroyd-B fluid was studied by an improved Distributed Lagrange Multiplier/fictitious domain (DLM) method. The sedimenting behaviors of two particles are presented firstly, which shows that, when the particles are dropped in a viscoealstic fluid, the stable configuration is the one where the particles are aligned parallel to the flow direction when the Mach number M is less than 1 and the elasticity number E is greater than 1. This agrees well with the known experimental in Ref.[1] and simulation results in Ref.[2]. Our simulations also show that, as in Newtonian fluid, the sedimentation of the particles will be accelerated due to the interaction between particles in a viscoealstic fluid.