Abstract: Horizontal migration of ammonium nitrogen in seashore saline soil on the coast of the Laizhou Bay was studied.The results show that ammonium nitrogen was moving horizontally at a speed that varied with the distance(0-20 cm)from the tracer source and the content of NH₄+ was also reduced gradually in power function due to adsorption by soil colloid.Horizontal migration was mainly determined by saturation of the soil adsorption of ammonium nitrogen,but its velocity was controlled by the concentration gradient and soil water potential gradient and moreover,in a sharp positive relation with the soil moisture content showing an exponential function.The concentration of ammonium nitrogen in horizontal migration decreased with the increase in unsaturated soil water diffusivity in power function.