With the development of ultra-precision machining technology, complex fluid is increasingly utilized. The analysis of ultra-precision machining fluid field is characterized by complex geometry, diverse constitutive equation and free boundary flow, which results in unsatisfactory analysis if adopting traditional numerical method. Based on general characteristic of fluid field, a robust and widely adaptable fluid analysis method is proposed in this paper by applying D. G. Christopherson’s super-relaxation iterative method for nonnegative second order partial differential systems to ultra-precision machining fluid field analysis. Besides, taking magnetorheological finishing as an example, the numerical calculation of pressure field is conducted for the polishing area and it is revealed that the calculated pressure distribution has reasonable morphology and it extends from positive x axis to negative x axis, which agrees with the experiment results by Zheng Ligong et al. Moreover, the in-situ experimental measurement of normal pressure by Kistler sensor is conducted for immersion depth ranging over 0.1 to 0.3 mm, it is demonstrated that the relative errors of calculations against experimental results are all less than 20%, indicating that the proposed method is valid and accurate.