Abstract: In this paper, the calculation methods for the radar cross section ( RCS) of sea targets are described. The test method of RCS through a theoretical model is discussed. However, the condition relations that satisfy the test requirements and test distance relations in the case of fluctuating targets are also focused on. For the complex targets like ships, the calculation normally should follows the rules. Under the certain condit-ions, the average RCS of targets with complex shape are generally subject to the arithmetic sum of the mean RCS by local reflection area.