The recent high-pressure experimental discovery of superconductivity in (La,Y)H10, and (La,Nd)H10 shows that the ternary rare-earth clathrate hydride can be promising candidate for high-temperature superconductor. In line with this, my previous work on other rare-earth metals forming ternary hydrides has revealed them to be potential high-temperature superconducting materials as well. In this work, I theoretically demonstrate that the combination of actinide-metal thorium (Th) and rare-earth-metal lanthanum (La) with hydrogen can also form some ternary hydrides with cage-like structures to be stable at 200 GPa. Using the evolutionary algorithms, I have predicted the pressure-dependent ternary phase diagram of LaxThyHz. My calculations show that the hydrogen-rich phases such as (La,Th)H9 and (La,Th)H10 can be thermodynamically stable below 200 GPa. More importantly, the electron-phonon coupling (EPC) calculations show that the (La,Th)H10 could the potential superconductors, of which I4/mmm-La3ThH40 exhibits the large EPC constant λ = 2.46 with a highest transition temperature (Tc) of 210 K. Since there are few previous studies on ternary actinide hydrides, this work would greatly stimulate the further discovery of this type of ternary hydrides and provide useful guidance for the high-pressure experiment on them.