The invention discloses a determination method for Pyrifluquinazon residual quantity. The method is mainly used for determining the content of residual Pyrifluquinazon in complex matrix food and agricultural products such as cereal grains and animal derived foods. Homogeneous extraction of residual Pyrifluquinazon in samples is carried out by using acetonitrile or an acetonitrile solution containing 1% of acetic acid, after purification and concentration with a C18 / PSA solid-phase extraction column, gas chromatography-negative chemical ion source-mass spectrometry (GC-NCI-MS) detection is carried out, a corrected standard curve is established by adopting a blank substrate solution which does not contain a pesticide to be tested, and quantization is carried out by an external standard method. According to the method, the average recovery rate is 75.1%-80.2%, the average relative standard deviation (RSD) is 4.8%-8.0%, the detection limit is lower than 2.77 microg / kg, and the determination method has the advantages of easiness, convenience and quickness in operation, good impurity removal effect, high sensitivity, marked characteristics, good repeatability, and accurate qualification and quantization. The determination method can meet the technical requirement of countries such as Japan, European Union and South Korea for 0.01mg / kg residue limit in corresponding food safety testing, namely 'uniform standard', so as to provide powerful technical support for guaranteeing the food safety of Chinese people and the healthy development of export trade.