The improvement of the preparation method for carboxy methylation of konjac glucomannan (KGM) was proposed in this paper according to molecular structural characteristics of KGM. Carboxymethyl konjac glucomannan (CMK) were yielded by first blending KGM with etherification agent and then basifying and catalyzing in ethanol. Through single factor and orthogonal experiments, the effects of reaction conditions on degree of substitution (DS) and apparent viscosity (η) were investigated, and the optimum reaction conditions were obtained as follow: 55°C, pH12 for 3 hours. The results indicate that the maximal value of DS and η were 0.5278 and 15.57Pa•s respectively. The reaction mechanism for carboxymethyl of KGM was proposed and checked by infrared spectra. Meanwhile, it is showed that the properties of CMK were rather good in terms of hydrated rate and hydrosol transmittance.