Aiming at the problem of severe cumulative error in determining the grade of titanium-iron sand ore by chemical analysis, this study takes the Weiliu titanium-iron sand ore in Funing County, Yunnan Province as an example to systematically analyze the error sources and control measures of the key parameters for determining the grade of titanium-iron sand ore by chemical analysis. The research findings are as follows: (1) There is a significant deviation in the TiO? distribution rate of ilmenite obtained by phase analysis: It is difficult to achieve effective phase separation for ilmenite and titanium-iron mixtures and other titanium-containing minerals. TiO? from ilmenite, titanium-iron mixtures and limonite is mistakenly included in the TiO? distribution rate of ilmenite (77.50%), resulting in an overestimation of the grade. Through the micro-area analysis of scanning electron microscopy energy dispersive spectroscopy (EDS) and the calculation of titanium element distribution equilibrium, the true distribution rate of TiO? in ilmenite was determined to be 57.24%. Using this value can reduce the error by 35.39%. (2) The direct application of wet weight in grade calculation will result in an error of 28.57%. (3) The results of the micro-area composition analysis by scanning electron microscopy energy dispersive spectroscopy (EDS) showed that the measured content of TiO? in ilmenite (51.72%) was 0.94% lower than the theoretical content. The theoretical content was adopted in the general survey stage, while the measured values should be used in the detailed survey and exploration stages.Based on the above findings, three error control measures are proposed:①Chemical phase analysis combined with process mineralogical research methods such as scanning electron microscopy energy dispersive spectroscopy (EDS) to comprehensively determine the distribution rate of TiO? in ilmenite; ②The dry weight was measured by the water injection method and the large gravel was removed.③The content of TiO? in ilmenite was measured in the micro-area by scanning electron microscopy energy dispersive spectroscopy (EDS).