At least 30 people were arrested in police raids in December but Yang was overseas at the time.
The 51-year-old has not returned to face the criminal charges, but the police have obtained a court order to freeze his alleged "tainted property" in a separate civil case.
This includes a mortgage-free home bought for $1 million and several bank accounts, including one with $504,000.
Yang was identified through surveillance and tapped phone conversations and police allege he was a "very substantial wholesaler" of pseudoephedrine.
"The inference available is that his assets would have been funded, at least in part, through criminal activity," according to the police application on the court file, to which the Herald was granted access.
The documents show that Yang gambled millions of dollars at the casino despite having a "modest" declared income.
In the 19-month period leading up to the Operation Ghost raids, Yang had a "buy-in" figure of more than $2 million and a gambling turnover - the total of money spent and winnings - in excess of $14 million at SkyCity.
He earned just $4,217 over the same period, or $222 a month, according to Inland Revenue documents on the High Court file.
The Herald revealed in December that several other Operation Ghost targets spent millions of dollars at the casino. Their gambling records have also been examined.
A spokesman for SkyCity said the casino had co-operated fully with the police and the Department of Internal Affairs and "fully discharged" its legal responsibilities, which he could not elaborate on because of legal restrictions.
"We take our responsibilities in this area very seriously. We place a very strong emphasis on surveillance and security, spending millions of dollars on this each year. We work very closely with the police and other enforcement agencies."
The assets will be restrained under the Criminal Proceeds (Recovery) Act. The law essentially forces someone to prove how an asset was paid for.
These cases are determined by the civil level of proof, the "balance of probabilities", rather than the much higher criminal evidential threshold of "beyond reasonable doubt".
Zhi Wei Yang, 51
• Alleged to have supplied pseudoephedrine, but avoided arrest as he was overseas.
Police have restrained his assets including
• A mortgage-free home purchased for $1 million
• Several bank accounts holding $79,000, $36,000, $72,000 and $504,000
• 33 pieces of jewellery, including a $43,000 diamond ring and a $33,000 pearl pendant
• More than $10,000 in cash
• SkyCity Casino records show Yang had a gambling turnover of more than $14 million in 19 months. Over the same period, he earned $4,217, according to Inland Revenue records.
