The invention relates to a preparation method of a small-size 
transition metal chalcogenide two-dimensional 
nanosheet. The method is characterized in that the 
powder of a block is treated as a 
raw material; a 
polymer is used as an additive, and 
polymer assistant ball milling is performed to obtain 
transition metal chalcogenide two-dimensional nanosheets with different sizes and different components. The method comprises three steps of weighing high polymers and 
polymer assistant ball milling prepared blocky 
powder; performing ball milling, separating, water adding, uniformly mixing and movingout; performing 
gradient centrifugation to obtain products with different sizes; purifying to remove excessive polymers. With the adoption of the method, the problems such as low yield, non-uniform appearance and complex processes of a current preparation method of a current small-size 
transition metal chalcogenide two-dimensional 
nanosheet can be solved; the method has the advantages of being high in yield, simple in processes, high in generality, easy to control processes,and the like; the prepared small-size transition 
metal chalcogenide two-dimensional 
nanosheet can be applied to differentfields, such as the fields of catalyzing, photoelectric and biomedicines.