The invention discloses a dynamic precision detection method under a complex motion state of a five-axis machine tool based on a double-ball-bar. The method comprises the following steps of step S1, determining the motion trajectory of a tool tip point; determining a tool attitude change process and planning the tool attitude; and step S3, respectively using high and low feed speeds to measure, and respectively calculating positive and negative peak values, a range, a standard deviation and an absolute average error of a detection result under two feed speeds as evaluation indexes. The dynamicprecision detection method provided by the invention comprises a richer motion state and a motion mode, and helps to detect and evaluate the dynamic precision of a five-axis numerical control machinetool more quickly, accurately and comprehensively; the parts affected by dynamic errors in tool tip point offset are separated by means of differential measurement, so that the impact of the dynamicperformance can be extracted, and the influence of geometric errors as miscellaneous errors in the dynamic performance evaluation can be reduced.