A portable trombone stand has a base and a post. The base can be placed over a plane stably and has multiple legs radially mounted around the base. Each leg has a pivoting end pivotally mounted in the base. The post is perpendicularly mounted securely on the base and has an instrument bracket mounted slidably on the post. The instrument bracket can be fastened on the post via a fastener and is able to be embedded in a cylindrical bore of a trombone to hold the trombone in position. Eventually, the portable trombone stand can be put into a cylindrical bore of a trombone, then put the portable trombone stand and the trombone into a case altogether. In this manner, the trombonist can conveniently carry the box to move around.