The mechanism of production increasing for the pinnate horizontal well is analyzed with the simulation technique. It is pointed out that the whole horizontal wellbore spreading widely and evenly in coal layers makes the stratum pressure drop evenly and fast, which increases the chance of desorption and diffusion and area controlled. This is the basic reason that the pinnate horizontal well can increase production. How such stratum parameters as permeability, Langmuir constants and adsorption time constant affect the gas production for the pinnate horizontal well is also studied with numerical simulations. Either for the vertical well or the pinnate horizontal well, bigger stratum permeability, steeper relative permeability curve, smaller residual gas saturation, higher gas content and stratum pressure are more favorable for gas production increasing. Langmuir constants decide the change of desorption quantity and influence the gas production through changing the extent of steep of isothermal adsorption curves in the pressure dropping area. The adsorption time constant only influences the time that gas production arrives at the maximum value for the vertical well, but it almost has no influence on the gas production for the pinnate horizontal well because the equivalent adsorption time constant is reduced.