The cross-field diffusion coefficient (D⊥) at the edge in the HT-7 tokamak is close to the Bohm value when the line average electron density ranges from 1.5×10 19 to 3.0 × 1019m-3. The energy profile of the particles is derived directly from the Hα (Dα) line shape; the dissociative excitation of molecules is dominating when the local electron temperature is above 10eV. By means of the Monte Carlo method the Dα line shape is also simulated. We find that the molecular dissociation contributes to 57% of neutral atoms and 53% of emission intensity in front of the lirmiter, and 85% of neutral atoms and 82% of emission intensity in front of the wall. The influence of atomic and molecular processes on the energy balance is discussed for the scrape-off layer (SOL), and the power loss from molecular dissociation is found to be 6 × 104kW at the SOL. The ion Bestein wave (IBW) can effectively suppress the magnetohydrodynamic behaviour,the fluctuation levels and the turbulence; the D⊥ in front of the limiter declines from 0.84 to 0.2m2.s-1 and the particle confinement time rises from 9 to 12ms.