Wang, 26, eased to victory in the 48-kilogram weight division, lifting a combined total of 205kgs to the delight of the strong Chinese contingent in the 6,000-seat ExCel arena.
Lifting the heaviest weight in both styles of lift - the explosive one-phase snatch and the two-stage clean and jerk - Wang posted a total of 8kg more than silver-medal winner Hiromi Miyake from Japan.
By winning silver, Miyake went one better than her father and coach, Yoshiyuki, who won a weightlifting bronze at the 1968 Olympics.
Yoshiyuki said: "I have two children, so perhaps the other one can win a gold medal so we can complete the set."
Ryang Chun Hwa of North Korea took the bronze with a total of 192kg, edging out 17-year-old Sirivimon Pramongkhol of Thailand by just 1kg.
A tearful Pramongkhol, who stands just 4 feet 8 inches tall, later spoke to her father via mobile phone in front of several television cameras.
"He is encouraging me and says in another four years to try again," she said.
Fellow Thai Panida Khamsri, expected to be a strong medal contender, exited the competition early with three failures at 81kg in the snatch lift - 10kgs short of Wang's best weight - leaving the platform with what looked to be an elbow injury.
Wang was competing in her first Olympics, despite having won every international tournament she has participated in, after suffering major injury problems and missing out on selection for the Athens and Beijing Games.
The gold, China's second on the opening day of the Games, will come as relief for the selectors, who chose Wang in preference to 19-year-old reigning world champion Tian Yuan.
More women's weightlifting medals are expected to follow for China over the next 11 days even though they arrived in London without any of their Beijing gold-medal quartet.
"I hope this medal can give the other team members encouragement," Wang said.
- Hiromi Miyake