Objective To measure the spattering range of spatter produced by dental handpiece used for simulating dental preparation in dental clinic, so as to determine the safe hygienic distance, reasonable location of barrier and safe height of dental unit. Methods Dental preparation was simulated in a dental clinic of a tertiary general hospital, 5% methylene blue solution was used as indicator agent of spattering dyeing, horizontal and vertical spatter produced during dental diagnosis and treatment was collected with glass slides, spattering range was determined by common optical microscope observation. Results When dental handpiece used for simulating dental preparation, the farthest spattering distance in horizontal direction was 1 600 mm, vertical spattering height was up to 1 800 mm away from 1 000 mm of diagnosis and treatment manipulation. Conclusion The best safe distance between two dental units without physical barrier should be more than 1 600 mm, the minimum height of physical barrier between two dental units should be no less than 1 800 mm.