The advantage with high effectiveness and low risk of air ASW is due to the most of submarines are incapable of threatening the air ASW platform in terms of lack of anti-air weapons. Under this circumstance, ASW helicopter is still unable to overcome attack errors of torpedo causing by the uncertain situations in ASW operation. These Errors are such as detection, position estimate, water entry precision of torpedo, torpedo sonar detection, and the unpredictable of submarine evasive action, etc. that the randomness is then attached to air-drop torpedo scenario. In this study, the relationship between perused torpedo and evasive submarine is the aim with taking into account of randomness of both positions. Monte Carlo simulation is used to simulate (2000 runs) a given scenario, which considers the 35 knot torpedo attacking the various speeds' submarine. The initial positions are generated by the concept of CEP which follows normal probability of distribution. This study rules out using torpedo countermeasures by submarine that is the purpose to see the net evasion effectiveness. The result shows that as speed of submarine is increased to over 29 knot, the probability of torpedo hit (ph) is decreased to 0.4 and when it's over 32 knot then it is under 0.23. This result also implies speed is one of the critical factors for submarine in its torpedo evasive action. The productive contribution of this study is to reveal the relationship of air-drop torpedo and submarine showing the mean time for torpedo to intercept submarine is exponentially increasing as submarine speed is increasing and the ph is expressed as negative exponentially decreasing vs. the increasing speed of submarine.