Research conclusions:(1)The joist load distribution should be changed from the even distribution into the saddle － shaped distribution or ladder － shaped distribution． The coordinated effect of the pile foundation should be taken into account in calculation of the internal force for the joist． (2) Taking the calculation presented in this paper，the bending moment value in the span of the joist decreases by about 40% while the variation of the shear force is small． (3) The size and the reinforcement of the joist designed with the traditional calculation model should be further optimized．