PEKING, Aug. 20— A former Taiwan Air Force flight instructor said here today that he had willingly defected on Aug. 8 in his F-5 jet fighter in order to demonstrate his desire to see Taiwan and China peacefully reunified.
Huang Zhicheng, a 29-year-old major in Taiwan, said his landing on the Chinese side of the Formosa Strait was not forced, as the Taiwanese authorities had suggested. Instead, he said, his ''return to the motherland'' was carefully planned three months in advance.
Mr. Huang, who went by the name Peter Z. Huang in Taiwan, met with reporters this morning in the Great Hall of the People. He wore a new but slightly baggy Chinese Air Force uniform -blue trousers, green Mao-style jacket and Mao cap.
He said he enlisted in the Chinese Air Force last week. Yesterday, Zhang Tingfa, the Air Force Commander, appointed him deputy commandant of China's Aviation Academy with the rank of deputy divisional commander. A $360,000 Award
Mr. Huang said he had not thought about what he would do with the $360,000 that the Chinese Government had awarded him for defecting. He was the first Taiwanese pilot to do so since before the Cultural Revolution in the 1960's.
Mr. Huang has been an honored guest at receptions and rallies since the defection was disclosed three days after his Aug. 8 landing at the Fuzhou airport in the coastal province of Fujian, opposite Taiwan.
Chinese press reports to the outside world on the defection have been muted. However, Chinese officials appear to be using it internally to support the notion that Deng Xiaoping's program for the peaceful reunification of Taiwan and China is having positive effects despite the increased belligerence of the Taiwanese authorities since the election of President Reagan.
Although he was referred to as ''Comrade Huang'' during his meeting with reporters this morning, the defector said that he had not joined the the Communist Party. Outdated Chinese Arms
He said his goal was to help China develop its air force. ''After I came back I found out that the military equipment of my country is rather backward,'' he said.
Mr. Huang, who lived in a comfortable air-conditioned house and drove a car in Taiwan, said that ''people's lives are rather hard'' in China. ''However, I'm full of confidence in the future development of my country,'' he said.
Mr. Huang was somewhat reluctant to criticize Taiwan at the news conference, in contrast to statements about the island attributed to him in the Chinese press. But he said the Taiwanese authorities did not allow people to discuss politics.
He said he took off with a student pilot, Lieut. Hsu Chiu-ling, at about 8 A.M. on Aug. 8 to check him out on instrument flying. Lieutenant Hsu was in the back seat. 'I Told Him Not to Worry'
Mr. Huang said he told the student to lower his rear cockpit blinds so that he could concentrate on instrument flying. Then, Mr. Huang lowered the altitude to 400 feet and headed over the Chinese mainland at 650 miles an hour. When the student noted from his instruments that they were over the mainland, Mr. Huang reportedly replied, ''I know.''
''I told him not to worry,'' Mr. Huang said. ''He just said we should turn left and go back to Taiwan.'' Mr. Huang said that he decided to fly the lieutenant back when the student told him that he did not want to land on the mainland. ''There were two reasons why I flew him back,'' Mr. Huang explained. ''One was that his presence would affect the smooth landing of my plane. And secondly was the question of his own rights. People now all talk about human rights. So I took him back, although at that time I was already short of fuel.''
The student parachuted from the plane near the Taiwanese coast and Mr. Huang flew back across the Formosa Strait and landed at Fuzhou.