Aiming at the problem of inadequate supply of radioopaque markers,the preparation of high drug loading coated pellets of barium sulfate used as radioopaque markers for examining colonic transit function was explored,providing a reference for the clinical diagnosis and treatment of slow transit constipation.Firstly,extrusion-spheronization process was used to prepare the barium sulfate-loaded pellet cores,and the powder layering technique was applied to prepare the barium sulfate pellets.Then,the pellets were prepared by fluidized bed coating technology.The coating process and formulation parameters on the properties of the pellets were optimized by single factor test and orthogonal test based on the index of in vitro stability,roundness,and yield.Finally,transmission electron microscopy was used to observe the appearance,and the radiopacity and the influence factor experiment of high drug loading coated pellets of barium sulfate were investigated.The results show that the barium sulfate coated pellets are prepared with 3% EC ethanol solution as the coating solution,and coating weight increases by 7.5%.The obtained optimal coating process parameters are as follows:the flow rate of coating solution is 6 Hz,the atomization pressure is 3 MPa,the temperature of inlet air is 70 ℃,and the fan frequency is 30 Hz.Coated pellets of barium sulfate have high corrosion resistant property,and are stable in simulated gastrointestinal environment.The image density is gradually strengthened from inside to outside with satisfactory imaging,and coated pellets of barium sulfate are stable in the high temperature,high moisture and strong light conditions.The prepared high drug loading coated pellets of barium sulfate have good properties,the formulation is reasonable and the preparation method is stable.It can provide a new radioopaque marker with clear imaging,stable quality and low cost for clinical diagnosis.