PP in-reactor alloy exhibits complex composition and phase morphology. It seems very important to characterize the chemical structure of PP in-reactor alloy and its fractions, since its chemical composition and chain structure are closely related to the ultimate physical-mechanical properties. The conventional techniques adopted to physically fractionate PP in-reactor alloy were reviewed systematically, including single solvent extraction, multiple solvents extraction, temperature gradient extraction fractionation, temperature rising elution fractionation and cross fractionation analysis, etc. The basic principle and practical application of each method were addressed in detail by classic cases.