We have developed a simple time-bin phase encoding quantum key distribution system, using the optical injection locking technique. This setup incorporates both the merits of simplicity and stability in encoding, and immunity to channel disturbance. We have demonstrated the field implementation of quantum key distribution over long-distance deployed aerial fiber automatically. During the 70-day field test, we achieved approximately a 1.0 kbps secure key rate with stable performance. Our work takes an important step toward widespread implementation of QKD systems in diverse and complex real-life scenarios.