First, you need to add your UnionPay card to your PayPal account, and contact your card issuer to enable online payment service for this card.
When you're ready to check out at the merchant's website, simply select PayPal as your payment method and use this UnionPay card to fund your payment. PayPal will redirect you to an online banking page operated by UnionPay or your card issuing bank. On this online banking payment page, you can see exactly how much you'll pay in Chinese Yuan before making the payment ....
1. Read more detail from Paypal.com
2. Instruction from Baidu (Chinese)