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 (Vo(2)) kinetics. In this simulation, work rate in DLE was separated into steps that were regarded as constant-load exercises (CLEs). It was assumed that Vo(2) kinetics behaved exponentially at the onset and offset of each CLE, respectively. Vo(2) 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 Vo(2) values at the onset of CLEs at a given time (nt-Vo(2)) corresponds to Vo(2) excluding oxygen debt in DLE. The sum of Vo(2) values at the offset of CLEs at a given time (dt-Vo(2)) corresponds to Vo(2) related to oxygen debt in DLE. The total of net- and dt-Vo(2) values is equivalent to Vo(2) actually observed in DLE (gs-Vo(2)). As the oxygen requirement level is a steady-state value of Vo(2) in CLE, the oxygen deficit level can be obtained by subtracting Vo(2) 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-Vo(2)). Oxygen debt and oxygen deficit were calculated by integrating df-Vo(2) and dt-Vo(2) from the start of exercise to a given time, respectively. Gs-Vo(2) 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-Vo(2) 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-Vo(2) kinetics in the simulation.