The Terriers are short of attacking options with James Vaughan and Jermaine Beckford on the sidelines through injury.
Church will be at the John Smith's Stadium until 8 December and goes straight into the squad for their Yorkshire derby against Barnsley on Saturday.
Terriers boss Simon Grayson said: "Simon is a player we have monitored for some time and he adds genuine top level quality to our striking department.
"We looked at bringing him to the club during the summer, but at that stage Reading wouldn't let him out.
"The current strikers have done a tremendous job so far, but we've suffered some injuries in that area recently and we felt the time was right to bring Simon in - especially as James is suffering from a troublesome thigh strain.
"All being well he will train with the squad on Thursday and comes into my thinking for Saturday's game at Barnsley."