The performance of carboxymethylated lignin (CML) dispersant prepared from black liquor by carboxymethylation was studied and the optimal formulation of 40% Myclobutanil wettable powder was confirmed. The results showed that carboxyl groups were largely introduced into alkali lignin by carboxymethylated modification therefore the solubility and dispersibility of alkali lignin were greatly improved. The suspensibility before and after heat storage of 40% Myclobutanil optimal formulation were respectively 91.9% and 88.1% and the wetting time was less than 90 seconds those met the requirements of WP.