Potassium is a harmful element in ammonium molybdate and subsequent molybdenum products, and its content is usually desired to be as low as possible. Through exploring the effects of changing cooling mode, roasting temperature, mineral particle size, washing temperature, and adding Na2CO3 on washing potassium reduction, qualitative analysis of minerals in different stages of ammonium molybdate production process was carried out by ICP, spectrophotometer, and SEM-EDS while quantitative analysis was carried out by advanced MLA technology. The results showed that rapid cooling, increasing the temperature of water washing, fine grinding molybdenum calcine, and adding Na2CO3 can improve the effect of potassium reduction in water washing. However, increasing the roasting temperature was not conducive to the release of potassium in water in molybdenum calcine, and changing the particle size of molybdenum concentrate had no significant effect on potassium reduction in water washing. Because the potassium content in molybdenum concentrate was very low, the traditional phase detection method had some errors. Through MLA detection, it could be found that there are four potassium-bearing minerals in the ammonium molybdate production process, namely muscovite, orthoclase, anandite, and illite. The potassium releasing behavior of potassium-bearing minerals was analyzed and the difficulty of four potassium-bearing minerals entering ammonium molybdate products was as follows: orthoclase>muscovite>anandite>illite. The results of MLA analysis showed that the muscovite can decompose into orthoclase and anandite during the roasting process of molybdenum concentrate. The initial reaction temperature of decomposing mica into orthoclase was 727 K. As the most harmful mineral in the process of ammonia leaching potassium mineral, orthoclase was not only from the raw material of molybdenum concentrate but also produced in the process of high-temperature roasting. The transformed muscovite decomposed extremely easy and thus greatly improved the proportion of orthoclase in the subsequent washing and ammonia leaching process, which was extremely difficult to remove and hence the formed orthoclase was relatively easy to enter into the ammonia immersion compromised product quality. The research results are of great significance for the production and application of low potassium molybdenum products.