A network flow abnormality detection system and method for detecting at least one network packet to determine whether a flow condition of the network packet is abnormal. The network packet includes L bit data element values. The method is fetching M data element values in above-mentioned L bit data element values by data element value fetch unit, wherein M is an odd number and larger than 1; N parallel processing units receive and process above-mentioned M data element values; comparison module compares above-mentioned M data element values and a standard threshold to generate M comparison result values; sum unit sums above-mentioned M comparison result values to obtain a comparison sum value; determination unit compares the comparison sum value and an abnormality threshold, wherein when the comparison sum value is larger than the abnormality threshold, the determination unit determines the flow condition is abnormal.