Abstract: Solving method to equality constraint inversion with ill-posed constraint matrix is discussed,and rank-reducing processing method,which is proved equivalent to truncated singular value decomposition method(SVD),is proposed to solve this kind of problem.Further more,a united adjustment method with enhanced usability is also put forward,which can not only solve inversion with ill-posed constraint matrix,but also solve problems with master model ill-conditioned or rank-deficient when constraint model is ill-conditioned.Finally,through some well-designed cases,the methods are discussed,and some conclusions are obtained.