Owing to the status that the price of thermal insulating agent for liquid metal has been raising constantly in recent years, the present work investigated the properties of carbonized corn straw using as thermal insulating agent of liquid metal. The results showed that the carbonized corn straw possessed higher content of fixed carbon, smaller repose angle (or better flowing property) and lower heat conductivity coefficient compared to carbonized rice husk. Both the laboratory test and practical application of using carbonized corn straw as thermal insulating agent of liquid metal showed that it had a better thermal insulating performance, whereas a bigger collapse ratio and agglomeration were found. Thus, a satisfied application performance of thermal insulating can be achieved by using a mixture of carbonized corn straw and carbonized rice husk. The application of carbonized corn straw as thermal insulating agent of liquid metal not only develops a new effective way to use corn straw, but also contributes to decrease the production cost of metallurgical industries.