Low-density superalloys often exhibit low yield strength in the intermediate temperature range (300−650 °C). To enhance yield performance in this range, the CALPHAD method was used to design a new Co-based superalloy. The Co−30Ni−10Al−3V−6Ti−2Ta alloy, designed based on γʹ phase dissolution temperature and phase fraction, was synthesized via arc melting and heat treatment. Phase transition temperatures, microstructure evolution, and high-temperature mechanical properties were characterized by differential scanning calorimetry, scanning electron microscopy, dual-beam TEM, and compression tests. Results show that the alloy has low density (8.15 g/cm³) and high γʹ dissolution temperature (1234 °C), along with unique yield strength retention from room temperature to 650 °C. The yield strength anomaly (YSA) is attributed to high stacking fault energy and activation of the Kear−Wilsdorf locking mechanism, contributing to superior high-temperature stability of the alloy. The yield strength of this alloy outperforms other low-density Co-based superalloys in the temperature range of 23−650 °C.