Concurrent high temperature and drought are predicted to occur more frequently with global climate warming, although their interactive effects on crop growth, nutrient concentrations, and nutrient use efficiencies are still poorly understood. Therefore, an improved understanding of how high temperature and drought interactively affect crops is crucial for accurately predicting crop response to future climates. Herein, we examined effects of simulated high temperature and drought stress on tomato seedlings in growth chambers. Tomato seedlings were grown under two soil water conditions (well-watered and drought stress) and two temperature treatments (ambient temperature-26℃/19℃ (day/night) and high temperature treatment-42℃/35℃ (day/night) (7 days)). Biomass production and allocation, specific leaf area (SLA), nutrient (total nitrogen-TN, total phosphorus-TP) concentrations, photosynthetic nutrient use efficiencies (photosynthetic nitrogen use efficiency-PNUE, photosynthetic phosphorus use efficiency-PPUE) were examined. The results showed that individual and interactive effects of high temperature and drought treatments reduced the biomass of roots, stems, leaves, and the whole plant, and the combination of the two treatments had the greatest effect on the whole plant. The individual high temperature treatment significantly reduced the root mass fraction (RMF) and root shoot ratio (R/S), whereas drought stress increased the RMF, stem mass fraction (SMF) and R/S, but decreased the leaf mass fraction (LMF). Furthermore, high temperature induced declines in leaf TN and TP and root TP concentrations, but increased stem TP concentration. Drought reduced leaf and stem TP concentrations, whereas it increased root TN concentration. The interactive effects of high temperature and drought treatments on biomass allocation and nutrient concentration were similar with that of the drought stress alone. We found that high temperature and drought interactively reduced PNUE and PPUE, and the effect of drought stress on PPUE was exacerbated by high temperature. Hence, drought combined with high temperature may generate greater risks on crops under future climates.