Abstract: On the basis of the homotopy arithmetic, this paper puts forward a uniform model of nonlinear least square (LS) adjustment, which can be used not only for the nonlinear LS adjustment of the rank defect problems, but also for that of the rank full problems. For the initial value with later precision, it is shown by the actual nonlinear function examples that we can still get the precise original solutions by homotopy nonlinear LS method.