The research on the state of soil water potential adjacent to emitters (SWPAE) is the key to study soil water movement under subsurface drip irrigation (SDI). Distribution of soil water potential energy under SDI was studied by theoretical analyses and tests. The results showed that there were two kinds of SWPAE according to the relationship between emitter flow and soil water conductivity. The SWPAE equaled to the soil suction, which was negative, when emitter flow was not larger than the capacity of soil water diffusion. Otherwise, it was positive. Both theoretical analyses and tests showed that SWPAE was mainly decided by emitter rated flow and the initial soil water content in the same soil. Under a certain range of emitter flow, SWPAE increased with the increasing of emitter flow, while it would decrease with the increasing of the initial soil water content. On the basis, formulas were built to calculate the distribution of soil water potential under SDI, and effects of distribution of soil water potential on SDI system were brief analyzed.