The invention discloses a method for multistage sand prevention of ocean natural gas hydrate depressurization production. The method comprises a step S1 of adopting low production pressure difference to perform depressurization production, first decomposing and exploiting hydrate of an earth layer outside a sleeve pipe and close to a well, discharging mud and silty sand ingredients of the earth layer, and only making uniform sand which is good in grain size and good in sorting coefficient remain; a step S2 of performing filling outside a pipe, squeezing the mud-removed coarse sand belt to the periphery of a gravel layer to achieve an effect of a primary sand-blocking barrier; making a filling belt outside the pipe serve as a secondary sand-blocking barrier; a step S3 of selecting gravel with the dimension larger than a filling pipe outside the pipe by one grade to perform filling in the pipe, and making the filling layer in the pipe achieve an effect of a third-stage sand-blocking barrier; making an internal sand-blocking screen cloth serve as a fourth-stage sand-blocking barrier; and a step S4 of performing step type step-by-step enlargement of production pressure differential to a set value. The sand prevention problem caused by high mud content of an ocean hydrate layer and large pressure drop range is solved fundamentally, the problem of difficulty in forming a downhole filling belt sand bridge is solved through step type enlargement of production pressure differential, and the hydrate well productivity is improved.