In this work, we utilize femtosecond laser pulse shaping technology to study the role of chirp in generation and detection mechanism of Terahertz pulses with LT-GaAs photoconductive antenna. Experimental results show that the PC antenna excited with slightly up-chirped laser will generate THz pulses with higher peak amplitude, total power and broader bandwidth. In the detection process, similar behaviors have been observed. We use one dimensional Drude-Lorentz model to simulate THz generation and detection processes to analysis our experiment results. Finally, we use this coherently controlled THz-Time Domain Spectrometer to study the properties of several samples, such as fused silica, metal hole array and lactose. Experimental results show that we can utilize this spectrometer to get more reliable optical constants than the conventional approach.