We investigated the interaction between two phases by numerical simulation of a turbulent channel flow laden with heavy particles. We calculated the fluid phase turbulence by a large eddy simulation with a point-force two-way coupling model and tracked particles by the Lagrangian trajectory method. Six cases with different particle volume concentrations for three kinds of particles were simulated. The particle dispersion properties on the inter-phase interaction were presented in this first part. The simulations provided comprehensive instantaneous two-phase turbulent flow fields. The particle streaky and cloudy preferential distributions, which weaken with increased particle inertia, are suppressed by particle modulation of turbulence. Modulation of turbulence is stronger near the wall than in other regions, because particle volume concentration is higher close to the wall and modulation increases with local particle concentration. The streaky particle distribution structures near the wall disappear earlier than the outer layer cloudy structures as the particle mass loading increases. Particle-phase instantaneous velocity scatter distributions, characterized by a Y-shape changing to a A-shape from the viscous sub-layer to the central plane, are altered by particle modulation of turbulence. (C) 2010 Elsevier Ltd. All rights reserved.