The synchronous condenser (SC) installed in the ultra-high voltage direct current (UHVDC) converter station of a heavy load center (HLC) has a problem of close coupling between reactive power support capability and short-circuit current level, leading to conflicting performance requirements. Therefore, this paper proposes a comprehensive evaluation and optimization for instantaneous reactive power (RP) and short-circuit current (SCC) of SC in UHVDC converter station of HLC. Firstly, the time scale characteristics of RP and SCC of SC are analyzed. The difference of RP and SCC in time scale can be utilized to partially resolve the conflict between the two performance requirements. The reactive power increment coefficient and the short-circuit current coefficient are proposed as evaluation indicators for quantifying the instantaneous RP and SCC of SC at different time scales. Finally, a comprehensive evaluation and optimization of the SC’s instantaneous RP and SCC is proposed, based on the seagull algorithm. This approach aims to mitigate the contradiction between the SC’s instantaneous RP and SCC from time scale. The simulation results confirm the reasonableness and practicality of the comprehensive evaluation and optimization discussed in this paper.