In this paper，the extraction of rhubarb dye and the stability of rhubarb dye to heat and acetic was investigated. This paper investigated mordant dyeing of the wool fabric with metallic ions Fe2+，Al3+. And the single-factor experiment method and orthogonal experiments were used to study the optimum conditions of pre-mordant dyeing with aluminum ion. As a result, the stability of rhubarb dye to heat and acetic was very good. The optimum conditions of pre-mordant dyeing with aluminum ion was the bath ratio of 1:25, dyeing temperature of 90°C, ph value of 5, and the concentration of aluminum mordant was 5 percent of the fabric and the concentration of the natural dye rhubarb was 60 percent of the fabric.