A simple all-dielectric metasurface with symmetric structure, exhibiting strong toroidal dipole (TD) resonance and ultrahigh quality factor (Q-factor), is proposed. The physical mechanisms of the TD resonance are investigated by calculating the electromagnetic field and the scattering power of multipoles. Simulated results demonstrate that the Q-factor is up to 3.71 x 10(4) and the corresponding figure of merit is 636.7. Moreover, the TD resonance can be excited under both x- and y-polarized incident terahertz waves due to the symmetric structure. The remarkable performances make the proposed metasurface has feasible capability for biological and chemical sensing in terahertz range.