Legal analysis: it is not illegal to use it simply as an avatar, but illegal to use it as a trademark and advertisement.

Legal basis: People's Republic of China (PRC) National Flag Law.

Article 17 A damaged, defaced, faded or substandard national flag shall not be hoisted.

Article 18 The national flag and its design shall not be used as trademarks or advertisements, and shall not be used for private funeral activities.

Article 19 Whoever intentionally insults the people and the national flag of China by burning, damaging, scribbling, defileing or trampling in public places shall be investigated for criminal responsibility according to law; If the circumstances are relatively minor, the public security organ shall impose a detention of not more than fifteen days.