<p>In this work, the influences of surface layer slurry at different temperatures (10 °C, 14 °C, 18 °C, 22 °C) on wax patterns deformation, shrinkage, slurry coating characteristics, and the surface quality of the casting were investigated by using a single factor variable method. The surface morphologies of the shell molds produced by different temperatures of the surface (first) layer slurries were observed via electron microscopy. Furthermore, the microscopic composition of these shell molds was obtained by EDS, and the osmotic effect of the slurry on the wax patterns at different temperatures was also assessed by the PZ-200 Contact Angle detector. The forming reasons for the surface cracks and holes of thick and large ZTC4 titanium alloy by investment casting were analyzed. The experimental results show that the surface of the shell molds prepared by the surface layer slurry with a low temperature exhibits noticeable damage, which is mainly due to the poor coating performance and the serious expansion and contraction of wax pattern at low temperatures. The second layer shell material (SiO₂, Al₂O₃) immerses into the crack area of the surface layer, contacts and reacts with the molten titanium to form surface cracks and holes in the castings. With the increase of the temperature of surface layer slurry, the damage to the shell surface tends to weaken, and the composition of the shell molds’ surface becomes more uniform with less impurities. The results show that the surface layer slurry at 22 °C is evenly coated on the surface of the wax patterns with appropriate thickness, and there is no surface shell mold rupture caused by sliding slurry after sand leaching. The surface layer slurry temperature is consistent with the wax pattern temperature and the workshop temperature, so there is no damage of the surface layer shell caused by expansion and contraction. Therefore, the shell mold prepared by the surface layer slurry at this temperature has good integrity, isolating the contact between the low inert shell material and the titanium liquid effectively, and the ZTC4 titanium alloy cylinder casting prepared by this shell mold is smooth, without cracks and holes.</p>