Sims-Walker had 63 catches for 869 yards and seven touchdowns for the Jacksonville Jaguars in 2009, but his production slipped after that and he was released by the St. Louis Rams after four games last year.
Johnson, coming off three straight years with at least 1,200 receiving yards, missed most of last season with hamstring injuries. Johnson had arthroscopic knee surgery recently, but is expected to be ready for the beginning of the season. The Texans let previous No. 2 receiver Jacoby Jones depart for the Baltimore Ravens this offseason.