In the indirectdrive target compression process, filamentation instability should be considered seriously, especially light intensity fluctuation of size 10～100 μm on the surface of target, and a proper beam smoothing method must be adopted. A new method, using fiber system to stack chirped pulses, treating the composite pulses with angular spectral dispersing, depressing the high frequency fluctuation in the focal spot with the beam smoothing mechanism of focal spot at different time determining different spectral components, is proposed. Using Fourier transform method, the expression for the composite pulses dispersed by a grating is deduced. Simulation results show that the size of the focal spot increases with the number of color cycles and the basic pulse bandwidth in the dispersing direction. Through calculating the flux contrast including 95% focal spot energy with time, it is found that the optimal smoothing effect is achieved with one color cycle and 0.3～0.5 nm basic pulse bandwidth. This new kind of temporal beam smoothing technique has the advantages of simple configuration and adjustable focal spot performance, and is of important application value in improving irradiation uniformity on target surface.