Abstract: Falsehood or forfeiture occurs frequently on the water level indicating meters of the steam generator, and there is no appropriate way that can precisely identify the water level but through the experience of the operator on that condition, which grievously affects the judgment of the operator on operation state of the nuclear power plant. GMDH is a flexible and normally used method to establish complicated non-linear large system mathematics model, which makes good effects when dealing with non-linear objects. A method reconstructing the water level of steam generator with GMDH in the circumstance that the crevasse of primary stream pipeline appeared was described. In comparison with the emulation results, it shows that GMDH can reconstruct the water level of steam generator accurately. The outcome can meet the practical needs and give guidance on the safe operation of the marine nuclear power plant.