Abstract: The precursors of methanol synthesis catalyst have been prepared using different coprecipitation method, and the catalytic activity and stability were tested using differential fixed-bed reactor. The pH values of the precursors of methanol synthesis catalyst in the period of ageing , especially around the colour-turning point have been studied. At the same time the effect of reaction temperature and reaction pH on the time of colour-turning of precursors and catalytic activity have been investigated as well. It is shown that the pH values of the precursors of methanol synthesis catalyst in the period of ageing changes continuously, the pH values appear a minimum in the vicinity of colour-turning point, at the same time the activity of the catalyst has a sharp increase after the colour-turning point. It is predicted that the composition and structure of the precursors altered obviously after the colour-turning point. It is shown that from the test result increasing reaction temperature favors structure adjustment of precursors; while increasing reaction pH restrain the structure adjustment of precursors. The experimental results showed that co-current feed method was the best method. The activity and stability of the catalyst prepared from co-current method was higher than those prepared by other methods. The optimum pH range of precursor was 7.5～8.5 and the temperature should be higher than 80 ℃.