Linear chirped pulse generated by direct phase modulation can be used in chirped- pulse amplification system, which can produce ultrashort optical pulses with high pulse energy. The process of the linear chirped pulse generation, the amplification and transmission characteristics of the modulated pulse in fiber have been numerically simulated and experimentally studied. A 500 ps pulse at 0.69 nm bandwidth linear chirped pulse has been generated in experiment. A new method of generating shock ignition seed pulse is proposed. A seed pulse with high contrast is generated by modulating and compressing part of the pulse, which is verified by expriment. A stagewise pulse with 2∶1 intensity contrast after modulating and compressing a square pulse is generated to confirm the feasibility of generating stock ignition pulse using this method. This method may be used in the front end system of intertial confinement fusion (ICF) driver in the future.