Power phase sign is an important power transmission equipment, and it is usually hung nearby the ending point of power transmission line. Detection and recognition of power phase sign is very important to power transmission line inspection. A method of power phase sign detection and recognition based on image processing and pattern recognition is put forward. At first, the power phase sign image is preprocessed by graying, median filtering, dilating and eroding. Then, a saliency object detection method based on region conformance operator is used to detect the power phase sign in the preprocessed image..Finally, a matching method based on ASIFT operator is used to recognize the power phase sign. The results of experiments show that this method can detect and recognize the power phase sign, and it has better robustness, accuracy and validity.