To improve the operating comfort of the Nuclear Magnetic Resonance (NMR) grain quality analyzer as well as the work efficiency of the inspectors, this study utilized the Hierarchical Task Analysis (HTA) method to sort out the operating process of the grain analyzer, and constructed 2 key postures, upright operation, and upright stooping posture, based on Jack's Digital Human Model (DHM). Jack was used to analyze the visual domain, reachable domain, and comfort of grain inspectors. The results showed that the upright posture when operating the grain analyzer was relatively better than the standing with bending posture, and the inspectors were less comfortable working in the upright posture for a long period. Based on the results of the analysis, an improved design of the operating area and the overall arrangement of the grain analyzer was made, and the improved solution was analyzed, it was found that the comfort level of the instrument was enhanced after the improvement. The research indicates that Jack’s suggestions for improving the instrument and proposing new design forms from a human factors perspective can serve as valuable references for the design of future NMR grain analyzers.