Abstract: A new technique to generate high frequency repeated sine synchronous scan seed source was introduced, based on the method of phase locked loop and direct digital synthesize technique. Phase locked loop was used to realize synchronous track of sine scan signal and trigger light impulse. Modulation of frequency, phase, and amplitude was achieved by direct digital synthesize technique. Delay of scan time was achieved by phase modulation, while different scanning rate was achieved by amplification modulation. The circuit system can obtain stable sine synchronous scan seed signal with frequency as high as 250 MHz, and jitter lower than 10 ps. The design is confirmed to meet the expectation, and fulfill the high precision requirements of streak camera on seed source for frequency, amplitude and time jitter.