A transforming circuit between parallel data and serial data includes a current source, a clock input sub-circuit, and a parallel data input sub-circuit. The clock input sub-circuit includes a first clock signal terminal and a second clock signal terminal. The transforming circuit between parallel data and serial data also includes a clock control sub-circuit and a serial data output control sub-circuit. The clock control sub-circuit includes four switching elements. A first and a third switching elements are controlled by the second clock signal terminal, and a second and a fourth switching elements are controlled by the first clock signal terminal. The serial data output control sub-circuit includes a fifth switching element and a sixth switching element to speed up the falling edge of the output signal flip, a seventh switching element and an eighth switching element to limit the output signal amplitude. A transforming system thereof is also provided.