The invention relates to solid-free well-completion confining liquid and a preparation method thereof. The solid-free well-completion confining liquid is prepared from a weighting agent, a clay stabilizer, a corrosion inhibitor, a deoxidant, a pH modifier and water. The density of the solid-free well-completion confining liquid is 1.20g/cm<3>-1.68g/cm<3> at room temperature. The solid-free well-completion confining liquid has good heat stability, has good compatibility with reservoir fluid, has low corrosivity on downhole tools and pipe columns, and is non-toxic and pollution-free to the environment. The solid-free well-completion confining liquid has the advantages of good protection effect on reservoirs, good fluidity, small frictional resistance and low cost, and the devitrification temperature can be regulated and can be minimized to minus 50 DEG C.