A single-phase PV (PhotoVoltaic) grid-connected system based on STM32 is proposed. Firstly, the mathematical simulation model of maximum power point tracking based on incremental conductance method and islanding detection based on active frequency drift is established, and then, the prototype,which using STM32 as the core processor, adopting composite control strategy based on PLL and grid voltage front feed-forward compensation, including BUCK charge control circuit, interleaved flyback converter circuit, full-bridge inverter circuit, signal adaptation and detection circuit, is designed. Test results show that: the prototype is stable, reliable, and harmonic content THD and islanding detection time consuming meets the required of relevant standards.