Haber-Bosch thermal ammonia synthesis is of energy-intensive nature. Using solar energy for ammonia synthesis is idealized for both energy and environment problems, but remains great challenges. Generally, the diffuse solar flux and inefficient utilization cannot meet the energy demand for NH3 production. Here we develop a solar thermal avenue, realizing highly efficient solar ammonia synthesis over K/Ru/TiO2-xHx. The supported Ru is efficient for nitrogen activation because of the electron donation from TiO2-xHx and free from H-2 poisoning, because the interfacial TiO2-xHx accepts H atoms from Ru and then delivers them to the Ru activated N-2 to form Ti-NHx (x = 1-3) even at room temperature. When only irradiated with sunlight, this catalyst absorbs sunlight in the whole UV-vis-NIR region and reaches 360 degrees C by its plasmonic behavior, exhibiting a Haber Bosch thermocatalysis-comparable NH3 generation rate. This solar thermal approach with K/Ru/TiO2-xHx provides a promising renewable way for ammonia synthesis.