The co-slurrying technology of coal and organic wastewater, which achieves the simultaneous disposal and utilization of wastewater, has attracted extensive attention in recent years. The emission of coal gasification wastewater causes serious environmental hazards, because of its large amount, high organic content, and high toxicity. In the present study, two types of wastewater, namely, gasifier wastewater (GW) and wastewater from a secondary sedimentation tank (SW), were used to prepare coal water slurry (CWS), which was labeled as coal-GW-slurry (CGS) and coal-SW-slurry (CSS), respectively, with coal-deionized water-slurry (CDS) as a reference. The surface property of coal and the dispersing mechanism were characterized using zeta potential and contact angle analyses. Results showed that the fixed viscosity loading decreased with the addition of the two types of wastewater, and the decrease was more considerable with GW. All the slurries exhibited pseudo plastic behavior and thixotropy, with the following order: CGS > CSS > CDS. Wastewater, particularly GW, strengthened the stability of CWS. The influences of ammonium and volatile phenols on slurry viscosity were also investigated. The effect of ammonium was related to the pH value of the solution. The effect of volatile phenols on the range of wastewater organic content was limited. The stability of CWS was obtained by combining the result of ammonium with organic matter. Ammonium affected the surface charge of coal particles and changed the electrostatic repulsion between coal particles. The amphiphilic organic molecules enhanced the hydrophilicity of coal, which weakened the hydrophobic interaction between particles and thickened the hydration layer. Consequently, the agglomeration of coal particles was weakened.