Abstract: The principle about measurement of the effective delayed neutron fraction β_eff by modified neutron source multiplication (MNSM) method combining source jerk method was given. Firstly, the absolute reactivity β of ADS Venus 1# sub-criticality reactor measured by MNSM method is -2.235×10^-3. Under the same sub-criticality condition, the reactivity ρ/β_eff in β_eff measured by source jerk method is -0.291 5 . The effective delayed neutron fraction is 0.007 667 by comparing ρ/β_eff with ρ. The effective delayed neutron fraction of MCNP is 0.007 783, which corresponds with the experiment result within 2%.