The hybrid catalyst prepared by physically mixing a commercial methanol synthesis catalyst and a solid acid dehydration catalyst was used for slurry phase dimethyl ether synthesis from syngas. It was found that the addition of dehydration catalyst resulted in a significant synergic effect on the overall syngas conversion. But, the excessive addition of dehydration catalyst could not enhance the synergic effect but instead depressed the whole reaction rate. It was also proven that this phenomenon existed when the methanol catalyst was used for low temperature water gas shift reaction. When the fine powder in hybrid catalyst was sieved away, the special phenomenon disappears and the conversion profile is the same with that in gas phase. It is proved that the presence of the fine and superfine powder could be a primary cause resulting in low catalyst activity. The better activity and stability of the hybrid catalyst can be realized by carefully choosing the catalyst particle size and improving the catalyst strength.