A passive coherent beam combination of two nanosecond amplifiers is realized by using an all-optical feedback loop. The width of the combined pulses is 9.7 ns, and the pulse repetition frequency is 2.023 MHz. With the least mismatch between pulse period and time of the cavity round trip in our loop, the visibility of far-field coherent patterns is more than 71%. The dynamics of passive phase locking is studied, and the established time of phase locking of two pulsed amplifiers is at least 10 cavity round trips in the all-optical feedback loop.