Abstract: The purpose of this experiment was to study the variation of maize root around flowering for fully understanding the genetic mechanism of root development under field conditions and to offer theory basis for genetic improvement of root in high yield and quality agricultural system. A BC4F3 population (187 lines) derived from Ye478 (with big root system) as the donor, and Wu312 (with small root system) as the recipient was developed. QTL for shoot dry weight (SDW) and root related traits in maize were identified by composite interval mapping of PLABMQTL software at the tasseling stage (VT stage, 10 days before silking) and early filling stage (R2 stage, 15 days after silking) under field conditions. Totally, 27 QTLs are detected for controlling root dry weight (RDW), total root length (TRL), lateral root length (LRL), axial root length (ARL) and axial root number (ARN). The contribution of each QTL varies between 52%-157%. Two important regions are detected on chromosome bin 602 and 1004 with controlled shoot dry weight, total root length, lateral root length and axial root number, and eight common QTLs are found at the both growth stages. There are specific genetic mechanisms for different root types at pre and post flowering stages, and the QTLs detected for root related traits are important to the formation of shoot growth of maize. These QTLs are helpful to understand the genetic basis of maize root under the field condition and offer the basis for further genetic improvement by MAS.