Limit-cycle-oscillation (LCO) is a ubiquitous feature in low to high confinement mode transition. We propose a double-source (heat and turbulence) prey-predator model of heat pulse induced LCOs in the edge plasmas. It is shown that the development of the radial electric field is a combined process of turbulent thermal and momentum transports. The causality relation between the turbulence intensity and the radial electric field reverses during the transport channel transfer. A numerical study reveals that the appearance of LCOs can be explained as a transition from a 'forced' oscillation to an 'intrinsic' oscillation of the edge plasmas. It is also found that there exists a critical equilibrium pressure gradient, above which the transient LCOs become stationary ones, i.e. a steady I-phase may be sustained.