Large amounts of sludge are produced in China each year. Its safe disposal and the recycling technology is the only way to solve the problem of sludge pollution, in which the sludge solidification technology is very important. Since the hygroscopic property and self-hardening property of paper sludge ash are important factors for developing cheap and effective sludge curing agent formulations, the research is practically valuable. The present research studies the basic engineering properties of paper sludge ash, its PH value, heavy metals in the extracting solution, hygroscopic property, microstructure and shear strength. The results show: the PS ash was weakly alkaline; the extracting heavy metals are of little pollution; hygroscopic property decreases with increasing pressure and there is a minimum water absorption; shear strength decreases as the water content increases.