Pushing Higher, page-42

How does a company qualify for the ASX200?
To be included in the ASX200 a stock must satisfy three conditions:

• The stock must be listed on the Australian Securities Exchange as an ordinary or preferred stock.
• The stock must satisfy liquidity requirements. Liquidity basically means how often the stock is traded and at what volume, indicating how easily an investor can buy or sell the stock. For the ASX200, the stock must have a certain level of liquidity, however the liquidity cannot be dominated by a small group of investors.
• The stock’s float-adjusted market capitalisation must also satisfy the requirements of the index. In the ASX200 that generally means that the company’s float adjusted market capitalisation must be amongst the 200 biggest on the ASX. The market capitalisation cannot include large strategic holdings or issuing of new shares.

Note that these three conditions are required for inclusion into the ASX200, however if an existing ASX200 company falls outside of the conditions temporarily, it does not mean that it is immediately excluded from the index. The index is rebalanced quarterly.

https://www.wise-owl.com/investment-education/asx-200-explained-what-is-the-asx-200