The rationality of Marxist theory that the social basic contradiction is the basic motive force and the class struggle is the direct motive force for social development lies in that the social basic contradiction solves social basic justice, namely reasonable social wealth distribution, which is the groundwork for social development, while the class confrontation and struggle is the most direct way to realize social justice. People's essential needs and class concept are impersonal and measurable, so we can make a quantitative analysis of them from the perspective of class analysis, which is a scientific method.