In this talk, I'll show the exact result of one loop hexagon integral in six dimensions. The integral can be interpreted as the volume of a 5-dimensional simplex in hyperbolic space. These simplices can be dissected into orthoschemes, a special type of simplices, whose volume has been well-studied. Therefore one can compute the volume of a general hyperbolic simplex by adding up all the orthoschemes produced in the dissection procedure.