We explored the relation between FWHMs of single pulses in a sample of GRB (Gamma-Ray Burst) light curves and durations of the GRBs. Based on a sample of 108 single_peaked GRB light curves, we fitted these sample data with Kocevski, Ryde & Liang (2003) model. A sub-sample containing 59 pulses with χ2T≈BWa, where T is the duration, W is the FWHM， a and B are constants. Our result shows that there does exist a proportional correlation between the logarithm of FWHMs and the logarithm of T90 (duration containing from 5% to 95% of the total fluence of a GRB) of GRB light curves with a correlation coefficient R=072.The proportional correlation between the logarithm of FWHMs and the logarithm of T50 (duration containing from 25% to 75% of the total fluence of a GRB) is more tight with a larger correlation coefficient R=093.Our finding shows that the light curve structure is correlated to the GRB duration. A larger FWHM corresponds to a longer GRB.