The main difference between Penglai Shahekou Airport and Penglai Airport lies in its size and use. Generally speaking, Penglai Shahekou Airport is a small airport, which is mainly used for flight test, training and life-saving services at sea. Penglai Airport is a large civil international airport, which is mainly used for flight test, training and tourism services.

1. Size difference: Penglai Shahekou Airport is a small airport, and Penglai Airport is a large civil international airport.

2. Different uses: Penglai Shahekou Airport is mainly used for flight test, training and life-saving services at sea, while Penglai Airport is mainly used for flight test, training and tourism services.

To sum up, the difference between Penglai Shahekou Airport and Penglai Airport mainly lies in its size and use. Penglai Shahekou Airport is relatively small, mainly used for flight test, training and life-saving services at sea. On the other hand, Penglai Airport is bigger and has more functions, mainly used for flight test, training and tourism services.