The main objectives of this research were to study the effects of sustained deficit irrigation (SDI) and partial drying of root zone (PRD) on yield and water use efficiency of squash (Cucurbita Pepo, L. Oto) crop. To fulfill these purposes, a field study was conducted in the experimental farm of Faculty of Agriculture, at Moshthor, Benha University, Egypt, for the two successive seasons of late summer (2016 and 2017), under both drip surface (DSI) and subsurface irrigation (SSDI) systems. Five irrigation treatments were undertaken. The first (FI-100%) was corresponding to full crop water requirements (FWR), and soil water deficit was replenished to field capacity when 50% of the available water was exhausted, depending on root depth which was predicted by a root depth model. The second treatment was corresponding to 80% of the FWR (SDI-80%), the third one was corresponding to 70% of FWR (SDI-70%), the fourth one was corresponding to 70% of the FWR and partial drying of root zone (SDI-70%+PRD), and in the last treatment (SDI-50%), the crop was irrigated at 50% of full water requirement FWR. In the treatment (SDI-70%+PRD), the root zone was irrigated partially but from alternate laterals. The results show that surface drip irrigation (DSI) resulted in lower WUE and lower yield of squash than the sub-surface drip irrigation (SSDI), although with the subsurface drip irrigation system water consumption is less than with the surface drip irrigation by 5 %. The treatment (FI-100 %) resulted in both the highest WUE and squash yield either with surface or sub-surface. The treatment SDI-80% resulted in WUE and yield not significantly different from FI-100%. SDI-70%+PRD resulted in WUE and yield almost equal to those achieved with SDI-80%.