【Objective】Based on the relation between low irrigation limit and yield, water use efficiency of tomato in under-mulching-drip irrigation in greenhouse, the optimal combination of low irrigation limits in the earlier and latter stages was studied.【Method】A field plot experiment was conducted in greenhouse and multiple regression analysis was used to deal with the experimental data.【Result】Low irrigation limits at earlier and latter stages influenced mutually water requirement and yield of tomato. Low irrigation limit at latter stage had more important effect on total water requirement than that at earlier stage, meanwhile low irrigation limit at earlier stage affected more significantly the tomato yield than that at latter stage. There was a parabola regression relationship between yield and water use efficiency. When tomato yield was 9.69×104kg·ha-1, the minimum of water use efficiency would be 62.28 kg·m-3.【Conclusion】Considered various factors, saving water, increasing yield, improving water use efficiency et al, it is advantageous to gain high yield when the soil water suction of low irrigation limits in earlier and later stage is 20 kPa and 60 kPa respectively. It is more important to enhance water management at earlier stage than that at latter stage. The results will enrich water regulation theory in under-mulching-drip irrigation in greenhouse.