It is a big challenge to apply laser induced breakdown spectroscopy (LIBS) to ocean in situ detection, but there are ample opportunities for LIBS development too. In the present work, laboratory investigations of LIBS on natural seawater at different pressures from 0.1 to 40 MPa were carried out. Pressure and laser pulse energy effects on LIBS emission were investigated. The result showed that enhanced LIBS emission can be obtained under elevated ambient pressure conditions. The line broadening of lines increases as a function of pressure. The time resolved LIBS emission results demonstrated that plasma emission is weakly dependent on the ambient pressure during the early stage of plasma and the pressure has a significant influence on the plasma form during plasma evaluation at a later stage of plasma. The obtained results suggested that the LIBS technique has the potential to be developed as an in situ chemical sensing technique for ocean applications.