In order to study the mortar performance of different mineral admixtures and cement composite cementitious materials, F class II fly ash, natural volcanic ash, and S75 slag powder are used to replace medium heat cement with 10%, 30%, and 50% respectively to form composite cementitious materials. Experimental studies are carried out on the fluidity, setting time, compressive strength, and hydration heat release of mortar with a water binder ratio of 0.5, and a cement sand ratio of 1:3, and the basic properties of mortar with different combinations of cementitious materials are compared. The results show that when the substitution amount is 10% ~ 50%, the fluidity of the mortar mixed with fly ash increases by 3.2% ~ 22.5%, the initial setting time is delayed by 11.2% ~ 20.4%, the final setting time is delayed by 13.3% ~ 43.5%, and the hydration heat release after 7 days is reduced by 7.4% ~ 39.7%; The fluidity of the mortar mixed with natural volcanic ash decreased by 3.2% ~ 21.9%, the initial setting time was 8.4% ~ 24.6% ahead, the final setting time was 5.3% ~ 20.0% ahead, and the hydration heat release in 7 days decreased by 2.9% ~ 25.4%; The fluidity of mortar mixed with slag powder decreased by 1.1% ~ 6.4%, the initial setting time is delayed by 8.4% ~ 28.8%, the final setting time was delayed by 9.6% ~ 25.1%, and the hydration heat release in 7 days was reduced by 4.8% ~ 30.1%. At a dosage of 10%, the compressive strength of the 90 day old mortar mixed with fly ash is close to that of pure cement. The compressive strength of the mortar mixed with slag powder at 28 days and 90 days increased by 1.6% and 2.4% respectively compared to pure cement. However, at other dosages and ages, the compressive strength of the mortar of the three combination cementitious materials shows a decrease, and the strength decreases with the increase of the dosage. The research conclusion can provide reference for the selection of cementitious material systems in concrete engineering.