NOVELTY - A fuel cell system load reduction comprises determining target power generation amount of fuel cell module (S1); increasing flow rate of oxygen-containing gas supplied to cell module (S2); reducing power generation amount of cell module (S3); reducing flow rate of fuel gas supplied to cell module; reducing flow rate of water supplied to cell module (S5); reducing flow rate of oxygen-containing gas supplied to cell module (S6); and detecting whether power generation amount of cell module reaches target power generation amount or less.    USE - Method for fuel cell system load reduction.    ADVANTAGE - The method improves the performance of tracking the load at the time of load reduction.    DETAILED DESCRIPTION - The fuel cell system load reduction comprises determining target power generation amount of fuel cell module; increasing flow rate of oxygen-containing gas supplied to cell module; reducing power generation amount of cell module; reducing flow rate of fuel gas supplied to cell module; reducing flow rate of water supplied to cell module; reducing flow rate of oxygen-containing gas supplied to cell module; and detecting whether power generation amount of cell module reaches target power generation amount or less. The fuel cell system comprises fuel cell module for generating electricity by electrochemical reactions of fuel gas and an oxygen-containing gas; fuel gas supply apparatus for supplying fuel gas to cell module; oxygen-containing gas supply apparatus for supplying oxygen-containing gas to cell module; water supply apparatus for supplying water to cell module; power converter for converting direct current electrical energy generated in cell module to electrical energy; and control device for controlling power generation amount of cell module.    DESCRIPTION OF DRAWING(S) - The drawing is a flow chart showing the operation method at the time of load reduction of fuel cell system.    Determining target power generation (S1)    Increasing oxygen-containing gas (S2)    Reducing power generation (S3)    Reducing water (S5)    Reducing oxygen-containing gas. (S6)