The invention relates to a synthesis method of rare earth doped quartz glass raw material powder. According to the method, rare earth and aluminum co-doped silicic acid sol is obtained with a silicon tetrachloride hydrolysis method and then is subjected to long-term ageing treatment at the normal temperature or is subjected to high-temperature and high-pressure ageing treatment in an autoclave to shorten the ageing time; aged gel is subjected to dewatering, hydroxyl removal and granulation, and uniformly-doped white powdery quartz glass raw material powder is finally obtained. The prepared rare earth and aluminum co-doped quartz glass raw material powder has the characteristics of low probability of crystallization. The method can be applied to preparation of large-mode-field silica fiber core rods with a sintering method.