The emerging quantum cryptography technology puts forward new requirements for lasers. To meet the requirements, an internal modulated semiconductor laser with high speed is developed. By using a special pulse shaping circuit designed, an input trigger pulse is divided into two pulses by a fan-out circuit. The two pulses pass through a delay circuit to produce different delay. The two signals are turned into a short pulse signal by a logic circuit. An RF amplifying circuit is used to drive a laser diode. The output laser pulse frequency can reach 1 GHz, the pulse width is less than 24 ps, time jitter is less than 12 ps and the -10 dB spectrum width is only 0.7 nm. Wavelength and power of the output laser have high stability. The laser designed can meet the requirements of a high-speed quantum key distribution with 1 GHz frequency.