1. Credit rating: The credit rating of bonds is a key indicator to measure the default risk of bonds in the market. Major credit rating agencies (such as Standard & Poor's, Moody's and Fitch) evaluate the credit status of bond issuers and give corresponding ratings. The lower the credit rating, the higher the default risk.

2. Default probability: Default probability refers to the possibility of bond default. It can be estimated by historical data, market conditions, financial indicators and other factors. Generally speaking, the higher the default probability, the greater the default risk of bonds.

3. Interest spread: Interest spread refers to the difference between the yield of bonds and the yield of risk-free assets (such as treasury bonds). The spread can reflect the market's expectation of bond default risk. If the bond spread is high, it means that the market risk perception is high.

4. Bond price: Bond price can also partially reflect the risk of bond default. When the default risk of bonds increases, investors' demand for bonds will decrease, leading to a decline in their prices. Lower bond prices mean that the market is worried about its default risk.