Among many physical models, the theoretical research of partial differential equation model of magnetohydrodynamics has developed rapidly and gradually become the hotspot of international applied mathematics, among which the existence, uniqueness, stability, boundary layer and asymptotic mechanism are the main contents of the research. Because the MHD system is of complex structure, it requires dimensionless treatment before solving the MHD system numerically. This paper gives the specific forms of continuity equations, momentum equations, magnetic induction equations and energy equations, and the system of MHD equations was analyzed undimensionalized.