Ab initio calculations of lattice constants, lattice stabilities of HgX (X=S, Se, Te) at different electronic temperatures (Te) have been performed within the density functional theory (DFT). We find that the lattice constants of HgX increase and the phonon frequencies reduce as Te increases. Especially the transverse-acoustic (TA) phonon frequencies of HgX gradually become negative with the elevation of the electron temperature. That is to say ultrafast intense laser induces lattice instabilities of HgX and athermal melting appears for the increase of laser intensity. What is more, with the X atom number increasing, the critical electronic temperatures of HgX are decreased in sequence. This result would be helpful for understanding the athermal melting processes for femtosecond laser micromachining.