Although there are still controversial opinions and uncertainty on application of SiCf/SiC compositecladding as next-generation cladding material for its great oxidation resistance in high temperaturesteam environment and other outstanding advantages, it cannot deny that SiCf/SiC cladding is a potentialaccident tolerant fuel (ATF) cladding with high research priority and still in the engineering design stagefor now. However, considering its disadvantages, such as low irradiated thermal conductivity, ductilitythat barely not exist, further evaluations of its in-pile behaviors are still necessary. Based on the selfdevelopedcode we recently updated, relevant thermohydraulic and mechanical models in FROBA-ATFwere applied to simulate the cladding behaviors under normal and accident conditions in this paper. Even through steady-state performance analysis revealed that this kind of cladding material couldgreatly reduce the oxidation thickness, the thermal performance of UO2eSiC was poor due to its low inpilethermal conductivity and creep rate. Besides, the risk of failure exists when reactor power decreased. With geometry optimization and dopant addition in pellets, the steady-state performance of UO2eSiCwas enhanced and the failure risk was reduced. The thermal and mechanical performance of theimproved UO2eSiC was further evaluated under Loss of coolant accident (LOCA) and Reactivity InitiatedAccident (RIA) conditions. Transient results showed that the optimized ATF had better thermal performance,lower cladding hoop stress, and could provide more coping time under accident conditions