Density pump-out phenomena are frequently observed in tokamak plasmas during central electron heating. On Experimental Advanced Superconducting Tokamak tokamak, we systematically investigated the plasma density response to variations in electron cyclotron resonance heating (ECRH) and neutral beam injection (NBI) power in electron heating dominated plasmas. It was observed that elevating EC or NBI power resulted in core density reduction. Interestingly, for comparable modifications in core electron temperature, NBI-induced density changes were more pronounced than those from ECRH. Simulation results indicate that both before and after increasing the heating power, density gradients strongly drive trapped electron mode (TEM), which partially explains the experimental observations. Furthermore, the impact of NBI power on ion temperature gradients could alter the dependence of temperature gradient-driven TEM on electron temperature gradients. We also observed that, under high-density conditions, the pump-out induced by EC power modulation was strongly reduced compared with the low-density case, but was markedly restored after impurity injection. This behavior can be understood as a modification of the dominant turbulence mode in the core plasma following impurity injection, with subsequent ECRH enhancement reversing this modification and consequently leading to elevated particle flux. These findings elucidate the physical mechanisms underlying density pump-out induced by high-power core heating in tokamak plasmas.