The purpose of the present study was to determine by simulation whether oxygen deficit kinetics in decrement-load exercise (DLE) starting from a low exercise intensity is related to the oxygen uptake (Vo₂) kinetics. In this simulation, work rate in DLE was separated into steps that were regarded as constant-load exercises (CLEs). It was assumed that Vo₂ kinetics behaved exponentially at the onset and offset of each CLE, respectively. Vo₂ at the onset of CLEs increases at the same time and becomes a recovery phase step-by-step corresponding to the decrement of work rate. The sum of Vo₂ values at the onset of CLEs at a given time (nt-Vo₂) corresponds to Vo₂ excluding oxygen debt in DLE. The sum of Vo₂ values at the offset of CLEs at a given time (dt-Vo₂) corresponds to Vo₂ related to oxygen debt in DLE. The total of net- and dt-Vo₂ values is equivalent to Vo₂ actually observed in DLE (gs-Vo₂). As the oxygen requirement level is a steady-state value of Vo₂ in CLE, the oxygen deficit level can be obtained by subtracting Vo₂ at the onset of CLE from the steady-state value. The oxygen deficit level at a given time was added in all CLEs. This is oxygen deficit per unit time (df-Vo₂). Oxygen debt and oxygen deficit were calculated by integrating df-Vo₂ and dt-Vo₂ from the start of exercise to a given time, respectively. Gs-Vo₂ increased, reached a peak, and decreased linearly until the end of the DLE. Oxygen deficit increased rapidly and showed a steady state. Oxygen debt increased linearly after a time lapse. The difference between oxygen deficit and oxygen debt changed like gs-Vo₂ kinetics. Therefore, it is concluded that if we consider the repayment of oxygen debt in the oxygen deficit in DLE, the kinetics of the oxygen deficit becomes similar to gs-Vo₂ kinetics in the simulation.