A degree day model was developed to predict the occurrence of Aphis craccivorain Lucerne using 3 years (2007-2009) data and validated with two years (2013-2014) data collected at research farm of ICAR-IGFRI Jhansi.The study indicated that the peak population of the aphid species can be predicted using heat accumulation starting with December 1st. Mean degree day (DD) required for aphids incidence was estimated to be 76 ± 4 degree days in lucerne fields. The peak aphids population was found at 199 accumulated degree days. The polynomial model fitted explains 72 per cent of the variability in lucerne aphids population. The model performance indicators viz mean absolute deviation, standard error, etc were within the acceptable range and the predictive capability of the model was fairly close to the observed values.