Abstract: The transient collisional excited Ni-like Ag 13.9 nm X-ray laser was simulated. Driven by two picosecond short pulses preceded by a 330 ps long prepulse, different short pulses of 1 ps, 2 ps and 3 ps were considered and for each case the angular characteristics of the output X-ray laser are presented in this paper. Detailed analysis shows that the (330 ps,1 ps,1 ps) pumping combinations delayed by about 500 ps can extract higher gains near critical surface and it works best. To get the effect of the first short pulse, X-ray lasers driven by only one short pulse following the same long prepulse was simulated and optimization was made. By comparing the optimized case of the two pumping scheme, the advantages of the two short pulses pumping scheme was indicated.