CHANGSHA, China — Inside a fishing gear store on a busy city street, the owner sits behind a counter, furiously tapping a smartphone to improve his score on an app that has nothing to do with rods, reels and bait.

The owner, Jiang Shuiqiu, a 35-year-old army veteran, has a different obsession: earning points on Study the Great Nation, a new app devoted to promoting President Xi Jinping and the ruling Communist Party — a kind of high-tech equivalent of Mao’s Little Red Book. Mr. Jiang spends several hours daily on the app, checking news about Mr. Xi and brushing up on socialist theories.

Tens of millions of Chinese workers, students and civil servants are now using Study the Great Nation, often under pressure from the government. It is part of a sweeping effort by Mr. Xi to strengthen ideological control in the digital age and reassert the party’s primacy, as Mao once did, as the center of Chinese life.

“We must love our country,” said Mr. Jiang, one of the top scorers on the app in Changsha, the capital of the southern province of Hunan. “We are getting stronger and stronger.”