The invention discloses a diesel locomotive adopting a traction mode of a flex-coil spring side bearing and a low-level diagonal draw bar. The diesel locomotive sequentially comprises a locomotive body, a locomotive frame and steering frames from top to bottom, and the locomotive body sequentially comprises a front machine chamber, a driver chamber, an electrical chamber, a resistance braking chamber, a clean air chamber, a power chamber, a cooling chamber and an auxiliary chamber; a main air reservoir and an accumulator box are respectively arranged on two sides of the middle part of the locomotive frame, each of two ends of the vehicle frame is provided with one steering frame, and a fuel tank and a traction pin are arranged in the middle of the lower part of the locomotive frame; the steering frames are secondary suspension steering frames, each steering frame comprises a frame body, wheels, primary damper springs and secondary damper springs, wherein the wheels are arranged under the frame body, each of the primary damper springs adopts a spiral steel coil spring and is arranged between the wheels and the frame body, and each of the secondary damper springs adopts a spiral flex-coil spring and is arranged between two sides of the frame body and the locomotive body. The diesel locomotive disclosed by the invention adopts the low-level diagonal draw bar steering frames, the structural arrangement of the diesel locomotive is not limited by circumscription and a wheel base, and the diesel locomotive can be well suitable for poor routes and high-frequency vibration for the upper part of the locomotive caused by high-speed running of the diesel locomotive.