Estimation of magnetic error field with alleviating fabrication tolerance of large superconducting magnets on JA DEMO reactor

•Evaluation of error field based on the accuracy of manufacturing of superconducting coils on JA DEMO were investigated.•The error field with all errors is 0.52 mT (ΔBTMEI /BT < 10-4).•The EFCC current was 200 kAT using two types of EFCC which are different toroidal angles outside the vacuum vessel.•The tolerance in coil fabrication would be mitigated by a factor of 2.5-5 compared with that of ITER on JA DEMO.