A spacecraft formation flying strategy with an Earth-Crossing Object (ECO) is proposed to avoid collision with the Earth. Assuming that a future conceptual spacecraft equipped with a powerful laser ablation tool has already rendezvoused with a fictitious Earth collision object, the optimal required laser operating duration and direction histories are accurately derived to miss the Earth. Based on these results, the concept of formation flying between the object and the spacecraft is applied and analyzed as to establish the spacecraft's orbital motion design strategy. The spacecraft formation flying strategy with ECO suggested in the current study successfully yields the spacecraft trajectory to maintain the required laser operating conditions with no additional fuel expenditure, which are very critical terms for achieving successful Earth impact avoidance. Also, the initial conditions for the spacecraft found in the current research can be used as a reference point to design the ECO rendezvous trajectory. The proposed strategy is expected to give useful insights into preparing more advanced future deflection missions.