In this paper, a wireless modular control strategy for input-series output-parallel (ISOP) inverter system is proposed to ensure equal sharing of input voltage and output current among the constituent inverters. Compared with existing control strategies for the ISOP inverter system, such as centralized control which restricts the modularity of the system and distributed control which realizes voltage and current sharing by means of connecting constituent inverter modules with several sharing buses susceptible to interference and reduces the reliability of the system, the proposed control strategy based on positive output-voltage-amplitude gradient can achieve fully modular design of the ISOP inverter system. Firstly, the control strategy is deduced according to the droop method, and the principle of the control strategy is analyzed in detail. Then the stability and design of the proposed strategy are also explored. At last, a two-module ISOP inverter system is tested in the laboratory and the experimental results verify the effectiveness of the proposed control strategy.