  We propose a scheme to determine the chemical potential and baryon number
density of the hadron-quark phase transition in cold dense strong interaction
matter (compact star matter). The hadron matter is described with the
relativistic mean field theory, and the quark matter is described with the
Dyson-Schwinger equation approach of QCD. To study the first-order phase
transition, we take the sound speed as the interpolation objective to construct
the equation of state in the middle density region. With the maximum mass, the
tidal deformability and the radius of neutron stars being taken as calibration
quantities, the phase transition chemical potential is constrained to a quite
small range. And the most probable value of the phase transition chemical
potential is found.
