Abstract: A mathematical model is established for working out the shallow formation fracturing pressure under the sea floor, taking the engineering characteristics of sea floor earth into consideration. Based on this mathematical model and with further combination of different field operating conditions, the models for calculating the minimum driving depth of riser under two conditions, i.e., taking the riser as only a path for normal drilling fluid circulation, and considering of axial load on the riser at wellhead, are also proposed. These models have been applied in a few oilfields in Bohai Gulf area, and the calculating results met the real conditions perfectly.