BRUSSELS -- Former Chinese Ambassador to the European Union (EU), Zhang Ming, has called for unwavering adherence to the right direction of China-EU relations, while the ties between two of the world's largest economies have suffered difficulties in 2021.

Taking the position as the 14th Chinese ambassador to the EU in October 2017, Zhang completed his four-year term and left Brussels during the weekend.

In a letter published by EUobserver on Monday, Zhang said he was convinced that developing China-EU relations is in the interest of both sides and the whole world, despite recent difficulties in bilateral relations.

"It's a must rather than an option to strengthen China-EU cooperation," he stressed.

The ambassador used four keywords to illustrate the basis on which a better relationship should be built on.

The first keyword is perception. "We need to stick to the right perception towards each other, which is the premise of healthy bilateral ties. The world is undergoing profound changes," said Zhang, who noted that China has always maintained a highly stable and positive EU policy since the two sides established diplomatic ties in 1975.

"Despite differences in systems, we sincerely believe that comprehensive strategic partnership remains our only appropriate positioning. We hope friends from the European side may also stand by such perception, and work with China to bring bilateral relations back to the track of cooperation," he wrote in the letter.

The second keyword is cooperation. There are already 70-plus dialogue and cooperation mechanisms between the two sides, and "we need to ensure win-win cooperation remains the mainstream of China-EU relations."

During the pandemic that hit the world in 2020, China became the largest trading partner of the EU. Looking into the post-pandemic era, China and the EU should cooperate to broaden common interests, which is vital for the economic recovery, green and digital transition, said the ambassador. He underlined the need to oppose protectionism and decoupling and jointly uphold multilateralism.

Multilateralism is Zhang's third keyword. "One lesson we can learn from the COVID-19 pandemic is that no country can face global challenges alone." China and Europe should uphold the central role of the United Nations in international affairs and reinforce the World Trade Organization-based multilateral trade system, he said.

Management is Zhang's fourth keyword. "China and the EU are different in history, culture, social system and development stage. It's only natural that we sometimes have differences. The key is how to properly manage them."

Pointing out that there is no magic formula, Zhang said "communication and mutual respect are surely better than unilateral measures and forced will."