The central topics on ultrafast terahertz spintronics are the interaction between terahertz photons and magnons, especially the interaction between terahertz photons and antiferromagnetic magnons. In view of the current researches and challenges faced in this field, this article reviews and summarizes the frontier research from the following three aspects: spintronic-based efficient terahertz radiation source, magnon excitation and manipulation with terahertz pulse, as well as the strong coupling between terahertz photon and magnon. We hope this review article can trigger interdisciplinary efforts that facilitate the invention of new protocols of active spin control and quantum phase engineering.