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The influences of laser pulses with negative frequency chirp and different pulse cycles on pair production are studied.By solving the quantum Vlasov equation,the momentum distribution and the number density of the created pairs are obtained numerically.It is found that the chirp rate can enhance the pair production rate in both supercycle and subcycle pulses.Moreover,there is an optimal cycle parameter corresponding to the maximum number density under the same chirp rate.The pair number density is sensitive to the cycle parameter when it is less than the optimal one.Compared to the positive frequency chirp,in the case of the negative frequency chirp,the optimal cycle parameter is increased.