Based on the theory of unsaturated soil water dynamics and characteristics of soil moisture movement under negative pressure irrigation, a moisture infiltration model was proposed. The time-varying rules of moisture infiltration at the vertical soil profile on condition of negative pressure irrigation were simulated by moisture infiltration model of HYDRUS—2D. Result showed that the relative error between simulated and measured value was 2%~4%, which was within a reasonable range. The soil moisture infiltration rules under the negative pressure irrigation can be described effectively by the model. Moisture infiltration with different soils (soil and matrix in Beijing area) and different sizes of emitters (radius varied 8, 10 and 12cm) were simulated. The simulation results indicated that emitter size was a significant influence factor for soil moisture infiltration. The initial moisture migration rate was faster with larger emitter than that with smaller emitter. Meanwhile, the delay at the beginning of infiltration was shorter with larger emitter. There was a positive correlation between infiltration rate and emitter size, and water infiltration rate increased with the increase of the radius of emitter.