The invention relates to the online slurry ash detection technology. The online slurry ash detection technology comprises steps that S1 of slurry preparation link, the to-be-detected slurry sample isfed through a feeding pump; S2 of slurry treatment link, through the drying dehydration method and the filtration dehydration method, the uniform and stable detectable state of the slurry is maintained; S3 of slurry detection link, X-ray fluorescence is employed for detection to acquire the detection map; S4 of data analysis link, the detection map is analyzed and calculated to acquire ash data ofthe slurry sample, and the data is outputted; S5 of slurry cleaning step, the detected slurry sample is cleaned. The technology is advantaged in that an intelligent controller is employed as a control core, in order to improve the representativeness of the slurry sample, a slurry mixing link is further included; in order to improve detection accuracy, the X-ray fluorescence is employed to detectdifferent detection points at least three times. The technology can detect the ash of the slurry sample in real time, the production process is guided and controlled in a timely and efficient manner,the product quality is maintained stably, and product index requirements are met.