We demonstrate the generation of coherent and collimated blue light (CBL) based on cesium (Cs) 6S_1/2(F = 4)→6P_3/2(F' = 5)→6D_5/2(F'' = 6)→7P_3/2(F' = 5)→6S_1/2(F = 4) diamond-type atomic system in a heated vapor cell. Two infrared pumping lasers with wavelengths at 852 nm (6S_1/2→6P_3/2) and 917 nm (6P_3/2→6D_5/2), provide step-wise excitation to the 6D_5/2 excited state, and induce strong two-photon coherence between the 6S_1/2 state and 6D_5/2 state. The atoms undergo a double cascade accompanied with the amplified spontaneous emission at 15.1 μm via the 7P_3/2 intermediate excited state, and produce a beam of 455 nm (7P_3/2→6S_1/2) CBL with highly spatiotemporal coherence through a parametric four-wave mixing process. We investigate the influence of experimental parameters such as polarization combination of the two pumping lasers, and their power, and the temperature of Cs vapor cell on the CBL. Especially, we add a beam of 894 nm laser operating at the 6S_1/2(F = 3) →6P_1/2 transition as repumping laser, which can pump atoms back to the 6S_1/2(F = 4) state from the 6S_1/2(F = 3) state, thus significantly improving the power of CBL. This technique of the CBL enhancement via optical pumping is also useful for the other alkali metal atoms.