Field experiments were conducted during the year 2019, in the experimental farm at the Faculty of Agriculture, Menoufia University, Shebin El-Kom, Egypt. The site of the experiment was 30' 54ºN and 31ºE. During the field experiments, the minimum night temperature ranged between 17ºC and 22ºC, and the maximum temperature during the day ranged between 30ºC and 36ºC. The objective of this study was the field evaluation of the subsurface drip irrigation system used in the tomato crop under different emitter discharge. To achieve this aim, a subsurface drip irrigation system was installed, which was tested hydraulically before the field study. It consisted of a main irrigation line (PVC) with an inner diameter of 51mm, a branch (PVC) with a length of 32m and an inner diameter of 36mm, and secondary irrigation lines (PE) with a length of 9m for each line and a diameter of 16mm installed. It has longpass emitters with 4, 6 and 8 L/h. Two distances were used between the emitters, 30 cm and 50 cm. Subsurface irrigation lines were buried at a depth of 15cm under soil surface. The field evaluation parameters were represented in measuring and calculating the following parameters: 1- Measuring and calculating the regularity coefficients of the points, which are (CV coefficient of variation as a result of manufacturing - EU broadcast uniformity). 2- Finding the crop coefficient values. 3- Measuring and drawing contour lines for moisture distribution in the soil profile under each emitter discharge. 4- Measuring and drawing contour lines for the distribution of salts in the soil profile under each emitter discharge. 5- The distribution of roots in the soil profile and its relationship to emitter spacing and the emitter discharge. 6- The surface area index of plant leaves and its relationship to the emitter spacing and the emitter discharge. 7- Water use efficiency of irrigation and productivity obtained for each treatment. 8- The physical characteristics of tomato fruits at each treatment. Finally, using longpass emitter at emitter spacing of 30 cm and emitter discharge of 8 L/h in order to achieve the lowest percentage of salt accumulation in the root zone. Using longpass emitters at emitter spacing of 30 cm and emitter discharge of 4 L/h due to obtaining the highest productivity per feddan and also obtaining the highest water use efficiency. Application of the subsurface drip irrigation system in the clay lands to obtain a large percentage of irrigation water saving in each irrigation and seasonal total irrigation water.