A method of dynamic control rod reactivity measurement for a reactor using a fission chamber as an out-of-reactor measuring instrument includes: maintaining the reactor in a critical state having a set output by inserting a reference control bank into a reactor core to a first depth; completely inserting the reference control bank into the reactor core from the first depth at a maximum allowable speed and immediately completely withdrawing the reference control bank from the reactor core at the maximum allowable speed, and measuring a first signal of the out-of-reactor measuring instrument from before the insertion of the reference control bank to after the withdrawal of the reference control bank; and determining static controllability of the reference control bank by adding residual controllability measurement value of the reactor to a first static reactivity of the reactor calculated using the first signal of the out-of-reactor measuring instrument.