Based on the construction data of continuous belt conveyors in shield construction，this paper evaluates two common calculation methods of slag weight （slag weight calculation based on loosening coefficient and slag weight calculation based on external additives ） to accurately manage slag in shield construction.According to the law of slag discharged from each ring in shield construction，an improved slag weight estimation method in shield construction was proposed.The results show that there is a big error in the slag weight calculation based on the loosening coefficient.When slag weight calculation based on external additives is used，the calculated value is always smaller than the actual slag weight，and the difference between them tends to be a definite value，which is also not strongly related to the two main formation conditions and the weighing mode of slag.The improved slag calculation method improves the accuracy of slag weight estimation，which is in good agreement with the actual slag weight in shield construction.