More than 6% of the world's total land area is impacted by salt. Most cultivated plants are sensitive to salt stress, and NaCl salinity, which results in ionic disturbance, osmotic and toxic effects, and which usually causes a great reduction in vegetative growth, rate of photosynthesis and an imbalance in plant nutrient uptake. Potassium (K) deprivation resulting from NaCl salinity, is expected to have a large and rapid negative effect on the rate of leaf expansion and final growth. Potassium (K), as one of 17 essential elements required for plant growth, participates in an array of processes, for example, potassium ions can be used as an activator for 60 different enzymes, promote photosynthesis, facilitate the transport of photosynthetic products, regulate the water potential of plant cells and stomatal movement. Plants subjected to salt stress are particularly prone to K deciency as within saline soils there may be less available K due to reduced K diffusion and poor root uptake. Therefore, K is frequently the main limiting element for plant growth and development during the ecological transformation of saline impacted land. Hence, the reasonable application of K fertilizers is the recommended treatment for enhancing soil K availability, stimulating plant yields and avoiding the deterioration of saline land. Hybrid pennisetum (Pennisetum americanum×P. Purpureum) is now widely regarded to have substantial potential as a bioenergy plant and a forage source for livestock production. It has been characterized by good stress resistance, fast growth and high yields. Hence, hybrid pennisetum is a suitable energy plant candidate for the transformation of coastal areas, which are considered as suitable sites for cultivation of energy plants, since they are widespread and cannot usually be used as farmland due to the high soil salinity. Therefore, in order to better guide the establishment of the bio-transformation of the Yellow River Delta saline lands using this potential energy plant, the effects of K nutrition on growth, photosynthesis and ion accumulation of the energy plant hybrid pennisetum, seedlings were examined under saline conditions. In a pot experiment, we investigated the effects of K⁺ level on seedling growth, ion concentrations in leaves and roots, photosynthetic characteristics, MDA (malondialdehyde) concentration and membrane permeability in the leaves of the hybrid pennisetum, under 0.5% NaCl to determine suitable levels of potassium supply to alleviate the salt damage of the studied species. The results showed the growth and photosynthesis of hybrid pennisetum seedlings were significantly inhibited under 0.5% NaCl conditions. However, the dry weight of shoots and roots, plant height and tillering number were significantly increased with the addition of K⁺, especially for 6 mmol/L of K⁺ under 0.5% NaCl. K⁺ supply significantly reduced the inhibitive effect of NaCl on plant height, tillering number, dry weight of shoot and root, and photosynthesis. The K⁺ supply also decreased the MDA concentration and membrane permeability, decreased the concentration of Na⁺ and increased the concentration of K⁺, markedly improving the K⁺/Na⁺ ratio of functional leaves. The results indicated that a supply of suitable concentrations of K⁺ (6 mmol/L) can significantly alleviate the inhibition of growth and photosynthesis caused by salinity in hybrid pennisetum. These findings would provide a theoretical basis for practical application when large-scale cultivation of hybrid pennisetum occurs on saline land.