Suffix-free padding rules is the sufficient and necessary conditions to preserve the collision security for MD iterated hash functions. We provide a suffix-free length encoding padding rule to the iterated construction hash function to present an efficient new hash transform. The new padding rule requires no change in the internals of a hash function, runs as efficiently as the original, and as usual it is collision-resistance preserving. The padding rule is better than some known padding rules in terms of the padding size and the message space.