The invention discloses a power frequency transformer-free three-phase-single-phase voltage transformation device. According to the three-phase-single-phase voltage transformation device, a single-phase-single-phase converter multi-module cascade structure is adopted to withstand three-phase power grid high-voltage; single-phase-single-phase converters at three phases are in cascade connection with one another and then are connected with in series with each other, so as to realize output, and therefore, a power frequency transformer can be omitted, and the three phase-single-phase voltage transformation device can be directly connected with a single-phase power supply network, and output voltage level can be improved; the single-phase-single-phase converter is mainly composed of a rectifying circuit, a bidirectional DC-DC conversion circuit and an inversion circuit. The single-phase-single-phase converters of the voltage transformation device are simple in structure, and therefore, the structure of the system can be greatly simplified, and two-way flow of the power of a three-phase power grid and a single-phase power supply network can be realized, and energy transmission efficiency can be improved, and thus, unbalance of the three-phase power grid can be avoided; and the converters can have reactive power and harmonic compensation functions through selecting proper control strategies, and therefore, electric energy quality of the three-phase power grid side can be improved, and reactive power and harmonic can be compensated for the single-phase power supply network.