Considering the limitation of investment cost, a unified optimal configuration method of voltage sag and harmonic resonance monitoring points is proposed in this paper. The observability indices of voltage sag and harmonic resonance are defined and quantified; Considering the observability of voltage sag and harmonic resonance as well as the cost economy of investment, the quantitative analysis method of the comprehensive performance of monitoring point configuration scheme is given based on analytic hierarchy process (AHP) method and fuzzy comprehensive evaluation method; Then, a unified optimal configuration model of monitoring points is proposed, which takes the highest comprehensive score of the configuration scheme as the objective and the number of monitoring devices not exceeding the limit as the constraint, which is solved based on the discrete particle swarm optimization algorithm; Finally, the unified optimal configuration of sag and resonance monitoring points is carried out based on IEEE-30 bus test system. The simulation results show that the proposed method can obtain the optimal configuration scheme of monitoring points, whose voltage sag observability, harmonic resonance observability and economy of monitoring devices are coordinated optimal under the condition that the number of monitoring devices meets the investment cost limit.