Abstract: Momentum equation of fluid mechanics is applied to calculate the flow force on 90 degree elbows, and the force on vertical shaft drainage pipeline was analyzed. The flow force on drainage pipeline can be divided into three cases, e.g. the hydrostatic pressure, the steady flow and the transient flow; the most dangerous situation appears during the transient flow. On the basics of these, the force on guide pipe support beams, welded straight pipe support beams and welded 90 degree elbows with horse are analyzed and calculated respectively. Using elbows less than 90 degree at the bottom of pipeline can reduce the force on support beam greatly, so as to reducing the cross section of support beams. Noticed that the influence of variation temperature in the shaft can be ignored when calculate the force on supporting beams. But special measures should be taken to eliminate the internal stress of pipeline caused by temperature changes.