The integrity of Marxism is the external extension of its internal logical structure. Interpretation of the integrity of Marxism must lie in the construction process and logical structure of Marxism. The category of labor is the overall and fundamental view of Marx and Engels on labor issues, which contains the logical whole of Marxism. The scientization of labor category is the epitome of the generation process of Marxist theories and becomes the main line of Marx and Engels' analysis on issues of evolution of the human society. The theoretical prospect of labor category is the reflection of the logical structure of Marxism and the hub connecting all theoretical modules of Marxism. Therefore, the category of labor is the logical kernal of Marxism, and provides a new perspective for presenting the internal structure of Marxism as a whole