An external linear electro-optic measuring system based on a poled polymer asymmetric Fabry-Perot multiple reflection film has been built, and the electric signals propagating on an indium tin oxide coplanar strip transmission line have been successfully measured. The nonlinear polymer spin coated on the high-reflectivity glass substrate was corona poled, thus an asymmetric Fabry-Perot film was fabricated based on polymer reflectivity and high reflectivity glass. The film standing-free technique and reflective configuration were adopted in this system. The principle of the system was analyzed by multiple reflection and index ellipsoid methods. The voltage sensitivity about 5 mv/ͱHz was obtained as 1 kHz sine input electric signals propagating on coplanar electrodes.