Optical sampling covering C band and L band based on sum frequency generation (SFG) in chirped periodically poled LiNbO3(CPPLN) is studied. Based on coupled-wave equations, the simulations and numerical computations of the transmission rate and bandwidth are carried out. NRZ sequences of the signal pulses with the transmission rate of 10 Gb/s are sampled. Distinct eye diagrams and quality factor Q are obtained by software-synchronized algorithm.The results show that arbitrary waveband inside C and L band can be sampled by tuning pump wavelength and that the bandwidth of the waveband is controllable by adjusting the waveguide length and the chirped coefficient of CPPLN waveguide. SFG in CPPLN waveguide used for optical sampling system has broader bandwidth and more flexible selectivity than that in PPLN waveguide.