The invention discloses a rock soil specimen ammonia gas saturation experiment method, which can realize fast high-efficiency saturation of rock soil specimens and comprises the following steps that adimidiate mold with the diameter being 1.0mm to 1.5mm greater than that of a standard specimen is developed; after the mold folding, a rubber membrane firstly sleeves inside the mold; sample soil bodies tamp the specimen in the mold in a layered way; then, the mold is put into a constant temperature box to be dried; after the specimen drying, the mold and the specimen are put into a sealed container to be vacuumized; then, sufficient ammonia gas is injected; before tri-axial experiment, the mold is put on a base of a tri-axial pressure chamber; the dimidiate mold is taken down; a pressure chamber cover is installed; confining pressure liquid is injected; confining pressure is loaded; the communicating vessel principle is used for performing water head saturation on the specimen; the waterhead difference is maintained to be 19.5cm to 20.6cm; when the water quantity for injecting the specimen is equal to the flowing-out water quantity, the continuous water head saturation is performedfor 30 to 40min; litmus blue test paper is used for sticking and coating flowing-out water until the test paper does not change the color, and the water head saturation stops.