For the first time, the cascading effects of self-phase modulation and second harmonic generation (SPM-SHG) in nonlinear optical medium were used to conveniently converted near-infrared ultrafast laser with fixed center wavelength into visible to deep-ultraviolet (DUV) laser with continuously tunable wavelength. When a β-BaB2O4 (BBO) crystal was used as the nonlinear optical medium, and a Ti:sapphire laser (800 nm, 38 fs) was used as the fundamental light source, the output wavelength had a tunable range of 225-460 nm, and the highest optical conversion efficiency reached 18.1% at 361 nm. For a 1030 nm fundamental light source, the shortest output wavelength was also 225 nm by one-step frequency conversion of BBO crystal. By further frequency conversions, the tunable wavelength can extend to vacuum ultraviolet (VUV) waveband, as short as 193 nm. These results demonstrated that SPM-SHG could be used as an extremely simple and effective frequency conversion method to obtain wideband tunable ultraviolet laser.