Based on research on production process of metanilic acid, a new idea of iron mud reducing nitrobenzene compounds was proposed, the optimum conditions to reduce 3-nitrobenzene sulfonic acid with iron mud were explored. In iron mud/Fe(II) reduction system, the main factors affecting the reduction of 3-nitrobenzene sulfonic acid are temperature, pH value, iron mud quantity, mass ratio between ferrous sulfate and the 3-nitrobenzene sulfonic acid, etc. The yield of metanilic acid is over 92% with temperature at 60oC, pH value at 8.0, iron mud quantity at 0.3g, and the mass ratio between ferrous sulfate and 3-nitrobenzene sulfonic acid at 1:1, which are the optimal conditions obtained by orthogonal experiment.