Unlike conventional lead ion (Pb2+) detecting methods, electrochemical methods have the attractive advantages of rapid response, good portability and high sensitivity. In this paper, a planar disk electrode modified by multiwalled carbon nanotube (MWCNTs)/chitosan (CS)/lead (Pb2+) ionophore IV nanomaterial and its matched system are proposed. This system presented a good linear relationship between the concentration of Pb2+ions and the peak current in differential pulse stripping voltammetry (DPSV), under optimized conditions of −0.8 V deposition potential, 5.5 pH value, 240 s deposition time, performed sensitive detection of Pb2+within sensitivity of 1.811 μA · μg−1and detection limit of 0.08 μg · L−1. Meanwhile, the results of the system in detecting lead ions in real seawater samples are highly similar to that of inductively coupled plasma emission spectrometer (ICP-MS), which proved a practicability for the system in detection of trace-level Pb2+.