The invention relates to a modified fuzzy sliding mode controlling method of a monopole three-phase photovoltaic grid-connected system, belonging to the control technical application field of a photovoltaic grid-connected system; the method has the advantages of strong robustness, good stability and rapid dynamic response speed; the method comprises the following steps particularly: firstly, feedforward compensation is led in to rapidly compensate the coupling part of d, q shaft current id and iq which are output by an inverter, thereby realizing rapid dynamic decoupling between id and iq; secondly, by controlling reaching law of lead-in index of an integral sliding mode controller, the dynamic performance of a sliding mode controlling system is improved, the response speed of the system at the initial starting stage is accelerated, and a system state trajectory is ensured to rapidly and smoothly enter in a sliding mode surface to move, wherein the sliding mode surface has good robustness to system interference; finally, a fuzzy control is led in to weaken the buffeting of common sliding mode control in the sliding mode surface, the output of the sliding mode controller is softened, and the stability of the system is improved.