A 348.9 nm intra-cavity frequency-doubling ultraviolet laser in blue laser diode pumped Pr∶YLF crystal is designed, in which a Z-folded cavity structure is adopted. A 444 nm blue laser diode with pump power of 1.4 W and a 469 nm blue laser diode with pump power of 1.5 W obtained are combined by a 45° combiner film as a pump laser for the Pr∶YLF crystal which has a length of 5 mm and a doping concentration (mass fraction) of 0.5%. In addition, the type I phase-matched LBO crystal is chosen for frequency-doubling. By optimizing the resonator mirror coating and structural design, we achieve a continuous ultraviolet laser output with a maximum power of 132.2 mW, a central wavelength of 348.9 nm, and an optical-to-optical conversion efficiency of 4.5% when pump power is the maximum.