We propose a method to generate high-quality broadband vector signal based on the combination of microwave photonics technology and predistortion algorithm. First, the simulation generates a 16-quadrature-amplitude-modulated (16QAM) signal with a carrier of 5GHz and a symbol rate of 1Gbaud. After loading the AWG output into our microwave photonics system, the signal is upconverted to 55GHz, and measure the output of the microwave photonics system with a realtime digital oscilloscope (RTDO). After signal demodulation and other operations, the error vector magnitude (EVM) value of the measured signal is 17.3%. Then, we use a predistortion algorithm to correct it. After predistortion, the EVM value of signal reduce to 10.8%.