Providing the plane Fizeau interferometer with a Twyman-model beam splitter, authors have accomplished a plane multipass interferometry which is easy to operate. The errors analyses point out that: such arrangement is realizable and valuable for practical applications. Experiments show that its sensitivity is 1~2 times higher than the conventional Fizeau interferometer for testing the polished uncoated optical elements, 7~9 times for high reflective coated sufaces.