properties that can distinguish strange stars from neutron stars? These are some interesting issues worth exploring, and are the main topics of this paper. Suppose that strange stars are the ground state of neutron stars, the conversion from neutron stars to strange stars can occur in different stages of the neutron stars’ lifetimes. There are two main regimes discussed in the literatures. One group of models suggests that such a phase conversion occurs in the very late stage of a neutron star’s lifetime, after it accretes sufficient amount of material to make the core density exceed the critical density for phase transition[@cd96; @bd00]. Another group of models, on which we mainly focus in this paper, suggests that the conversion occurs in the very early stage of a neutron star’s life time, i.e., during or shortly after a supernova explosion[@gen93dpl95aggs97], so that the observed radio pulsars might be strange stars. In the conventional strange star models, a crust composed of normal matter is usually assumed above a strange star’s bare quark surface[@afo86; @kwwg95], which tends to smear out the possible differences between the emission of strange stars and of neutron stars. An important issue raised in this paper which differs from 