The invention relates to a low-cost manufacturing method of a 700 MPa-grade cold-rolled high-strength steel and a thin steel strip based on cover annealing treatment. The 700 MPa-grade cold-rolled high-strength steel comprises the following chemical components: 0.15-0.20 percent of C, 0.20-0.50 percent of Si, 0.7-1.2 percent of Mn, not more than 0.023 percent of P, not more than 0.015 percent of S, 0.05-0.10 percent of V, not more than 0.015 percent of N, 0.022-0.035 percent of Al, not more than 0.004 percent of O and the balance of Fe and inevitable impurities. The invention also provides a preparation method of a cold-rolled high-strength steel strip (plate) of which the tensile strength is at the grade of 700 MPa. A steel strip which is subjected to hot rolling at a controlled rolling and controlled cooling condition is used as a raw material for annealing treatment and secondary cold rolling so as to prepare the steel strip which is more than 700 MPa in tensile strength, more than 8% in percentage elongation and good in formability, and the steel strip meets the requirements on steel for automobile welded tubes.