Abstract: The paper is concerned in the sourcejerk method u se d to measure the subcriticality, and the subcritical experiment facility, wh ich is used for the study on the neutronics of ADS, driven by external neutron s ource 252Cf. The effects of the location of neutron source and materia l buffer where is at the location of the pipe of proton beam and target of fissi onproduct dispersion on the subcriticality of reactor are studied by source jerk method.