Efficient broadband harmonic conversion has important application value in high power laser. However, it is difficult to achieve broad bandwidth and high efficiency at the same time in the traditional second harmonic generation (SHG). This paper proposes a novel broadband SHG scheme, which uses the space-time coupling effect to transform the temporally chirped pulse into a spatially chirped one, and then several spliced crystals are used to achieve efficient broadband frequency conversion. Simulation results show that for the spliced KDP crystal, the conversion efficiency of the fundamental harmonic reaches about 60%, for pulse bandwidth of 30 nm and central wavelength of 1 053 nm. Moreover, the frequency doubled light is still linear and broadband, and can be compressed as the fundamental pulse.