The premise of maintaining high fracture conductivity in channel fracturing is that the proppant pillar fully supports the fracture，but it is not clear whether the fracture can be fully supported by the proppant pillar with different thicknesses and diameters. Based on the elastic mechanics theory，a finite element model of the proppant pillar contacted with formation was established to study the optimal laying spacing between the neighbouring proppant pillars with different thicknesses and diameters under closure pressure，that is，the optimal laying spacing of the proppant pillar. When the distance between the adjacent proppant pillars is less than the optimal laying spacing，the proppant pillar can fully support the fracture，otherwise the fracture closes partially and the fracture conductivity decreases. Based on the optimal laying spacing and the material conservation laws，the optimal pulse time for clean fluid was calculated. The results show that the higher the closure pressure and the construction displacement are，the shorter the pulse time for clean fluid is. When the fracture width is larger，the pulse time becomes longer. In the process of the entire channel fracturing，the construction displacement should be increased and the pulse time for clean fluid should be reduced in high closure pressure reservoir，while the pulse time for clean fluid should be increased in low closure pressure reservoir.