The invention discloses a low-alloy high-strength hot-rolled steel strip suitable for the extremely cold area and a preparation method thereof. The low-alloy high-strength hot-rolled steel strip is prepared from the chemical compositions in percentage by weight: 0.06-0.10% of C, 0.6-0.7% of Si, 1.40-1.70% of Mn, 0.015-0.025% of Nb, 0.005-0.010% of Ti, 0.004-0.007% of Mg, less than or equal to 0.010% of P, less than or equal to 0.010% of S, less than or equal to 0.002% of Al, 0.002-0.005% of N, and the balance of Fe and unavoidable inclusions. The preparation method includes the following stepsof removal of S from molten iron through a KR method, removal of P and C through a duplex converter, an LF refining furnace, slab continuous casting, reheating of billets in a heating furnace, roughing and finish rolling, ultra-fast cooling, laminar cooling and coiling. According to the low-alloy high-strength hot-rolled steel strip suitable for the extremely cold area and the preparation methodthereof, the problem of the phenomenon of the uneven structure of rolled materials in the ultra-fast cooling process is solved.