Abstract: In order to solve problem of low feeding size into air chamber under the bed jig for refuse pre-preparation,the key parameters of SKT jig are upgraded such as discharging device,air chamber,sieve plate etc. upgraded SKT jig with maximum feed 200 mm has been successfully applied to refuse pre-preparation system in Yan’an Hecaogou second mine coal preparation plant. The application shows that average loss of clean coal carried in refuse is 0. 23%,and average loss of middings carried in refuse is 1. 99%,when separting lump raw coal 25~200 mm.