In this paper, we developed a method to determine absolute energy scale of DAMPE via measuring geomagnetic cutoff on cosmic ray electron and positron spectrum. The rigidity cutoff on cosmic ray electron and positron was calculated using IGRF-12 model and cosmic ray particle trajectory tracing code developed by Smart and Shea. Then we also measured cosmic ray electron and positron spectrum in MacIlwain L bin [1,1.14] based on over 425 days flight data of DAMPE. By directly comparing calculated geomagnetic cutoff with DAMPE measured result, we provide an estimation on absolute energy scale of DAMPE $1.25\%$ higher than expected at about 13GeV energy with uncertainty about $\pm1.75\%(stat)\pm1.34\%(sys)$.