The invention discloses an improved asphalt mixture immersion Marshall stability testing method. The improved asphalt mixture immersion Marshall stability testing method comprises the specific steps of sampling, standard water bathing, negative pressure water bathing, sealed water bathing and calculation of asphalt mixture Marshall stability water loss rate MS0 = {(MS3-MS2)/MS1} * 100%. According to the improved asphalt mixture immersion Marshall stability testing method, the test-piece immersion vacuumizing processing process is introduced to simulate the pumping effect of rainwater in a southern hot and humid area under the load effect of a vehicle, the erosion degree of water to an aggregate and asphalt interface is increased, and a field environment is life-likely restored. According to the method, a dried test piece is packaged by using a plastic sealing bag and is subjected to water bathing, water is isolated through the sealing bag, and erosion of the water to the dried test piece is eliminated. A novel calculation method is adopted, the stability damaging degree of the water is simply expressed, and the defect that an original immersion Marshall stability testing result is interfered by an asphalt aging effect is overcome.