Three-impulse-at-one-spot thruster is a device which initiates three igniters by logic igniting circuit, and achieves trajectory correction for various flight vehicles. The effects of different main charge amounts, thickness of sealing film and combustion chamber volume on sympathetic ignition of the igniters were analyzed. Results show that output performance improves by increasing main charge amount while sympathetic ignition taking place after excessive charge,so 175-200 mg charge amount is suggested. The sympathetic ignition is effectively prevented by increasing thickness of sealing film while excessive thickness brings too much energy loss, so 0.3 mm thickness of sealing film is suggested. The sympathetic ignition is effectively prevented by increasing combustion chamber volume while too large volume will result in excessive whole dimension, so 3.7 mL chamber volume is suggested.