To compare with the predictions of the transitional dynamical symmetry X(5) proposed by Iachello (2001 Phys.Rev. Lett. 87 052502), the critical behaviours of U(5)-SU(3) are studied in the space of two control parameters in the interacting boson model (IBM). A simple-shaped phased diagram has been presented. It is found that X(5) predictions cannot be exactly reproduced by our calculations and that the best agreement is close to the calculations with boson numbers N=11 and 12. By comparing with experimental data on X(5)-like nuclei, we find that X(5) predictions and IBM calculations can reproduce the energy ratios and E2 transition ones.