The invention discloses a low pressure casting forming method for an aluminum alloy motorcycle wheel rim, which is characterized in that: an aluminum alloy motorcycle wheel rim blank is designed according to a directional solidification principle in a metal solidification theory, so that the rim is solidified from bottom to top; the feeding gradient of the rim is progressively increased at a rate of two degrees from the junction of the rim and a spoke to an upper wheel flange, so that a rim feeding channel is smooth; and the top of the rim is provided with an annular blind riser, so that the feeding of directional solidification of the rim is realized, and the rim does not have a shrinkage porosity defect.