The invention discloses a three-phase separator. The three-phase separator comprises a shell body, an overflowing baffle, a gas outlet, liquid outlets, a gas-liquid inlet and a classification rotating blade, wherein a separating cavity is defined by the shell body, the overflowing baffle is arranged in the separating cavity and divides the separating cavity into a first cavity body and a second cavity body, and the height of the overflowing baffle can be adjusted; the gas outlet is formed in the top of the shell body, the liquid outlets comprise a water outlet and an oil outlet which are formed in the bottoms of the first cavity body and the second cavity body correspondingly, and the gas-liquid inlet is formed in the upper portion of the shell body; and the classification rotating blade is arranged below the gas-liquid inlet, communicates with the gas-liquid inlet and goes deep into the inner portion of the first cavity body. According to the three-phase separator, the structure is simple, operation is convenient, and the separating efficiency is high. The invention further provides an oil and gas well testing and measuring system and a combustion control method thereof. A Vx multiphase flowmeter is adopted, the surface flow rate of underground sample liquid is simply and rapidly measured, by using the three-phase separator, the underground sample liquid is separated efficiently, finally, the size of a fuel nozzle of a PID control combustor and the pressure of air compressed by an air compressor are blurred, and combustion treatment is more sufficient and safer.