The invention relates to a synthesis method of PODE (polyoxymethylene dimethyl ethers) and mainly aims to solve the problems of low catalyst activity and selectivity in technologies for synthesizing PODE from reaction materials including methanol and polyoxymethylene in the prior art. According to the synthesis method of PODE, methanol and polyoxymethylene are used as the raw materials and contacted with a PODE catalyst to react to produce PODE; the catalyst is modified metal ion modified sulfonic acid type polystyrene cation exchange resin including a crosslinked polystyrene framework and a sulfonic acid group; modified metals comprise at least one of IIA metals. Therefore, the synthesis method can be used in industrial production of PODE.