The invention discloses a preparation method for 2-(6-substituted-1,3-dioxane-4-yl) acetic acid derivatives shown in general formula I (refer to the description). The method is simple and convenient in technology, and the removal step of a protecting group can be eliminated, so that generation of by-product is reduced, aftertreatment is simple and easy to operate, and reaction yield is greatly improved; besides, ester with high steric hindrance, which is difficult to obtain in the prior art, can be prepared. The synthetic method provided by the invention reduces the cost, and is suitable for large-scale industrial production.