The simultaneous pharmacokinetic-pharmacodynamic modeling of xylazole were studied by gas chromatography (GC), high-performance liquid chromatography (HPLC), spectrofluometry, radioimmunoassay, electroencephalography (EEG) and electromyography (EMG) method. The pharmacokinetic data were analyzed by GC-HPLC RIA method, and the pharmacodynamic data were measured by ECG, EEG and EMG method. The parameters of pharmacokinetic-pharmacodynamic simultaneous modeling were estimated by cpu-pk-pdcomputer program on the basis of changes of acetylcholine (Ach), norepinephrine (NE) and ß-Endorphin (ß-Ep) levels after intramuscular administration in blood, CSF, pituitary and hypothalamus. We explained their sedation analgesic and muscular relaxation effective mechanism and their interrelation. The sampling and effect-quanlity assay were simulcast on same animals. The parameter of simultaneous pharmacokinetic-pharmacodynamic modeling of xylazole as follows: A. Parameters of simultaneous PK-PD modeling for blood kinetics-EEG: N(Hill coefficient)=0.10123, Keo=0.2209 min -1 , t 12Keo =3.14 min, E c50 =0.304 µg/mL, Emax=0.2214(%), AUE 1=0.02427 µg/mL·min, AUE 2=0.2140 µg/mL·min, r=0.9926; B. Parameters of simultaneous PK-PD modeling for CSF kinetics-EEG: N=0.9766, Keo=0.2209 min -1 , t 12Keo =3.1378 min, E C50 =0.3954 µg/mL, Emax=0.2214(%), AUE 1=0.1605 µg/mL·min, AUE 2=0.1835 µg/mL·min, r=0.9937; C. Parameters of simultaneous PK-PD modeling for blook dinetics-EMG: N=0.1379,Keo=0.2265 min -1 , t 12Keo =3.0596 min, E c50 =0.7804 µg/mL, Emax=0.8721(%), AUE 1=0.5357 µg/mL·min, AUE 2=0.5584 µg/mL·min, r=0.9989.