Salt lakes and seawater contain a large amount of sulfates and chlorides, which can cause degradation of underwater concrete structures from the outer surface to the inner core. According to the heterogeneous corrosion characteristics of mortar under sulfate and chloride attack, a series of tests, including X-ray diffraction, compressive strength, splitting tensile strength and Vickers hardness tests, were conducted on samples exposed to different corrosion conditions to investigate the evolution of phase composition and macro-and micro-mechanical properties of mortar. A Vickers hardness evaluation model was developed by modifying Logistic function. The results revealed that the corrosion products of sulfate and chloride decreased under combined sulfate and chloride attack. Moreover, the distribution of Vickers hardness along depth under combined attack could be divided into three phases, namely, ascending, descending and stable phase. The proposed evaluation model accurately described the Vickers hardness distribution of mortar in sulfate and chloride environment. Additionally, Vickers hardness was shown to be effective in analyzing the evolution of compression resistance in different corrosion depths. The research findings could provide some reference for durability evaluation and restoration of concrete structures.