The invention discloses thin-specification RE700MC steel prepared based on a fully headless thin slab continuous casting and rolling process and a preparation method of the thin-specification RE700MCsteel. The RE700MC steel is prepared from, by mass, 0.04%-0.06% of C, 0.15%-0.50% of Si, 1.3%-1.8% of Mn, 0.02%-0.04% of Als, 0.010%-0.06% of Nb, 0.04%-0.13% of Ti, 0.0020% or less of S, 0.012% or less of P, 0.005% or less of N and the balance Fe. The product thickness of the RE700MC steel is 1.0mm-3.5mm. The preparation method comprises the working procedures of raw material selection, convertersmelting, LF refining furnace refining, RH refining furnace refining, continuous casting, continuous rolling, induction furnace heating, finish rolling, cooling and curling. The RE700MC steel in the scheme has the advantages that mechanical performance is excellent, the plate size is stable, the inclusion spheroidization degree is high, and the microscopic structure is excellent. Meanwhile, the preparation method is short in technological process, low in energy consumption and cost and stable in product performance.