A same-polarization electrooptical-scanning laser imaging radar transmitting system for down-looking synthetic aperture comprises a laser, a half wave plate, an aperture diaphragm, a first polarization beam splitter, a first 1/4 wave plate, a first reflection mirror, a first electrooptical scanner, a first cylindrical mirror, a second reflection mirror, a third reflection mirror, a second electrooptical scanner, a second cylindrical mirror, a second polarization beam splitter, a second 1/4 wave plate, a fourth reflection mirror, a transmitter-telescope primary mirror, a high-voltage power source and a signal generator. The same-polarization electrooptical-scanning laser imaging radar transmitting system is capable of electro-optically scanning cross rails of the same polarization state and ultimately realizing parabolic equipotential line difference of two polarization orthogonal light beams at a far-field target, is used for scanning targets, simple in structure, free of mechanical scanning, small in size, light in weight, and particularly suitable for onboard or satellite-borne high-speed operating carrying platforms, and response speed for electrooptical phase modulation wave surfaces is fast and up to nanosecond level.