高手来指教一下

标准地道翻译:
天津是我国首都北京的门户，是全国第三大城市，渤海沿岸最大的港口
Tianjin,the third biggest city in China, is the portal of capital Beijing and the biggest port of Bohai Coast as well.

Tianjin is the gate of our capital Beijing,the third largest city of China,and is the largest harbor around the Bo sea.