The work aims to quantitatively analyze the load stability of palletized unit in the process of loading and unloading with forklift based on ADAMS simulation, so as to avoid the accidents caused by the loose or collapse of stacking during the loading and unloading of palletized unit load with forklift. Corrugated boxes were stacked in overlapping and in an interlaced way to reach a limit height of 2200 mm on pallet with kraft card board, forming the palletized unit loads without fixing measures such as wrapping and bundling. With the palletized unit loads formed by these two stacking methods as the research object, the ADAMS dynamic simulation model of handling with forklift was established, and the load stability was analyzed. From the simulation results, when the weight of cargo was 14 kg, the cargo offset and vibration acceleration were the maximum. At this time, the speed curve of the forklift and the experimental requirements verified the rationality of the simulation data setting. The position offset curve between the cargo and the pallet was extracted. In the overlapping stacking, the offset of the cargo along the direction of the fork tip reached a maximum value of 123.4 mm. The vibration acceleration curve of the cargo was extracted to evaluate the brittleness value of the cargo, and the brittleness value of the cargo should be above 60 to avoid damage due to vibration. No stacking collapse accident occurs in the target palletized unit loads formed by the two proposed stacking methods during the loading and unloading process with forklift, even though none of fixing measures such as wrapping and bundling are applied. However, cargoes at the upper layers of the unit loads have large position offset and vibration, which may cause the risk of loose stacking and damage to the cargoes. It is recommended to apply necessary measures such as wrapping and bundling.