The invention discloses a spherical internal detector for detecting petroleum transmission pipeline leakage. The detector comprises a spherical aluminum shell and a polyurethane foam layer outside the shell, wherein an electronic device is arranged in the aluminum shell and comprises an ARM (Advanced RISC Machines) processor, an IMU (inertia measurement unit), an A / D analog to digital converter, an SDRAM (Synchronous Dynamic random access memory) internal memory, an NAND Flash memory, a micro SD (Secure Digital) memory card, an anti-aliasing low-pass filter, a preamplifier, an electret capacitor microphone, a rechargeable lithium battery, a power supply module and a connection flat cable, wherein a digital triaxial accelerometer, a magnetometer and a gyroscope are arranged in the IMU. Theinvention has the advantages that the detector has high detection sensitivity, low preparation cost, a small size and low power consumption, is not easily blocked in a pipeline, is flexible to use and is widely applied.