Modulation strategies of the hybrid cascaded multilevel converter（HCMC） under different modes are studied. Firstly， to reduce switching frequency and losses of director switches， a novel asymmetrical square wave modulation at fundamental switching frequency is proposed. Under this modulation， the energy exchange characteristic between the wave shaping circuit and the outside system is analyzed， and then the range of the voltage modulation ratio and duty ratio under steady operation is derived. Secondly， a modified phase-shifted carrier-based pulse width modulation（PWM） with sub-module capacitor voltage balancing strategy is developed for the wave shaping circuits. Moreover， the direct current blocking mode and static synchronous compensator mode are also investigated， and it is pointed out that the modulation strategy under steady operation mode can be effective under the latter mode by amending the modulation reference voltage. At last， the effectiveness and feasibility of modulation strategies is verified by PSCAD/EMTDC simulation.