In order to determine the type of alkaline activator for gypsum-based slag cementitious materials, the fixed mass ratio of titanium slag and gypsum to 9: 1, and Na2SiO3, triethanolamine, Na2SiO3 mixed with triethanolamine were used to three activators. Then, nine groups of gypsum-based slag cementitious material test pieces were made with the dosage of alkaline activator 0.6%, 1%, and 1.2%, and the unconfined compressive strength was performed for 7 days. The experimental results showed that triethanolamine should not be used alone as an activator, the effect of compound Na2SiO3 and triethanolamine is better than that of Na2SiO3 used alone, and the 7-day unconfined compressive strength of the cementing material is higher than 1.5Mpa.