It is very important to obtain the temperature and heat flux distribution in the mould which can reflect the nonuniformity along circumferential direction and the changes of practical operation parameters for visualization of continuous casting process, on-line monitoring of strand quality and precise prediction of abnormality. In this paper, based on the data of continuous monitoring temperature in round billet casting machine, an inverse problem algorithm is applied to study the 3D heat flux field and the real 3D shell thickness profile in the mould which can reflect the nonuniformity of heat transfer along circumferential direction in normal production. The results indicate that under the course of normal production, the mould heat flux and shell thickness are various along the circumferential direction, and are influenced by the installation conditions of mould in caster. A “high heat flow region” occurs in the area 80-130 mm below meniscus, where the heat flux is obviously higher and more nonuniform than that in the area in middle and lower part of the mould. The heat flux profile along circumferential direction in the “high heat flow region” determines the profiles of shell thickness at different heights below meniscus to some extent, both of them have similar profiles, this provides theoretical basis for improving the billet surface quality and getting uniform shell thickness by analyzing and monitoring heat flux distribution in the mould especially in the “high heat flow region”.