Abstract: Based on the singular value decomposition(SVD)scheme,a new method for determining the mobility of bar assemblies considering the effect of loads is proposed.It mainly consists of the criteria for mobility of mechanisms and the method of how to distinguish transient assemblies.The independent modes of inextensional mechanisms and the states of self-stress are obtained by analyzing the equilibrium matrix.The criterion formulae for mobility of bar assemblies are listed.The results show that mechanisms would become stable structures when the vector of joint forces and the modes of inextensional mechanisms are orthogonal to each other.Transient assemblies are analyzed separately and the corresponding criterion formulae are obtained.Some typical examples are discussed.The conclusions are shown at the end,and the structural system is further classified.