Projective invariants for five coplanar lines have found many important applications in computer vision. Since there are many invariants for five coplanar lines and these invariants are relative to order of the lines

it is very difficult process to match the invariants from diffierent views. In this paper

we first derive the relations among all the projective invariants for five coplanar lines by using cross-ratio; then

we divide these projective invariants into five classes

any two of which being independent of each other; upon this

we derive two joint projective invariants for five coplanar lines which are independent of each other and irrelative to the order of the lines.