The invention relates to a cement grouting steel bar connecting structure of a precast concrete unit. The cement grouting steel bar connecting structure is characterized in that steel bars connected by adopting cement grouting are butted, wherein a first connecting steel bar is embedded in a first constructional element body, simultaneously the first constructional element body is provided with a grouting connection cavity, the connection end of the first connecting steel bar is arranged in the grouting connection cavity; the inner wall of the grouting connection cavity is provided with a concave-convex rough surface; an annular metal stirrup with a longitudinal connection bar is arranged at the periphery of the grouting connection cavity along the length direction of the steel bar; the connection end of a second connecting steel bar embedded in a second constructional element body is inserted in the grouting connection cavity of the first constructional element body and is opposite to the end of the first connecting steel bar; at least one of the end parts of the first connecting steel bar and the second connecting steel bar is provided with an anchoring head, the diameter of which exceeds the original external diameter; and gaps between the inner wall of the grouting connection cavity and the connecting steel bars are filled with shrinkage-free cement or cement mortar.