The invention discloses a thickness measuring system for an inner wall anticorrosive coating of a small diameter pipe. The system comprises a first measuring vehicle, a second measuring vehicle, a first signal processing vehicle, a second signal processing vehicle, third measuring vehicles, a power conversion vehicle, a battery vehicle and an electromagnetic positioning vehicle coaxially connectedin the small-diameter pipe from front to back, two adjacent vehicle bodies are connected by a hose, the electromagnetic positioning vehicle is provided with a mileage measuring mechanism at one end away from the battery vehicle, a flange is mounted on an input port of the small-diameter pipe, and a high-pressure gas pipe communicated with the small-diameter pipe is installed at one end of the flange away from the small-diameter pipe. The system has novel design, the signal processing vehicle is inserted between the three measuring vehicles, the signal transmission length and signal interference are reduced, the mileage measuring mechanism is used for recording the traveling mileage of a vehicle body, an external high-pressure gas source is used for pushing the I-shaped vehicle body, the power consumption of the vehicle body itself to install a driving device is reduced, and the duration of a battery car is prolonged.