Agro-forestry water-retaining agents are crucial agricultural materials for mitigating agricultural drought, yet the current industry standard "Agro-forestry absorbent polymer" (NY/T 886-2022) lacks effective evaluation indicators for their water retention performance, hindering the selection of suitable agents. To improve the evaluation of water retention in agro-forestry water-retaining agents, this research studied the energy types and states of water adsorbed or retained by these agents(hereinafter referred to as held water by agricultural and forestry water-retaining agents) by referring to soil water analysis methods in soil science and the First and Second laws of Thermodynamics. The water retention performance of agro-forestry water-retaining agents was analyzed from an energy perspective, and it was proposed that the internal energy loss(△U) of held water could serve as an evaluation indicator for water retention. Additionally, water retention experiments were conducted on four commercial agro-forestry water-retaining agents to verify the effectiveness of the evaluation indicators. The water absorption ratio, equilibrium time for water absorption, water loss rate, and thermal effects of four commercial agro-forestry water-retaining agents were tested and analyzed. The results indicated that there are four types of potential energy in the water held by agro-forestry water-retaining agents: solute potential energy (Es), matric potential energy (Em), gravitational potential energy (Eg), and pressure potential energy (Ep). Thermodynamic analysis showed that after water absorption, the entropy of the retained water decreased (dS<0), indicating the existence of external volume work (-pdV<0), while the increase in surface area of the retained water led to surface work (γdAs>0). The work-energy relationship revealed that the internal energy loss of water held by agro-forestry water-retaining agents(△U) is a key factor determining their water retention performance. The four commercial agents exhibited significant differences in water absorption ratios, with the highest reaching 545 g/g, and equilibrium times ranging from 6 hours to 1 hour. At 60°C, the water loss rates of the four commercial saturated agents were 1.48 g/h, 1.72 g/h, 1.97 g/h, and 2.19 g/h, respectively, compared to 2.41 g/h for pure water. When buried in red soil at 60°C, the water loss rates were 0.62 g/h, 0.94 g/h, 0.99 g/h, and 1.05 g/h, respectively, versus 1.33 g/h for pure water. Three distinct thermal effects were also observed during the water absorption process of the agro-forestry water-retaining agents. The soil water retention experiments with the four commercial agents supported the thermodynamic analysis results, and the thermal effect results were generally consistent with theoretical analyses. This study provides scientific evidence and technical support for the efficient utilization of agro-forestry water-retaining agents, contributing to alleviating agricultural water scarcity in arid and water-deficient regions.