The invention discloses a construction machinery hidden danger detection method for a power transmission line. The construction machinery hidden danger detection method comprises the following steps:acquiring images in a power transmission line channel and around the power transmission line channel in real time; making a data set of large construction machinery existing in a power transmission line channel, and randomly distributing according to a ratio of a training set to a test set of 4: 1; performing image preprocessing on the training set; processing the training set by adopting a multi-sample image synthesis method to obtain new training set sample data; training the new training set sample data by using a Faster R-CNN + FPN model to obtain a detection model of the hidden danger ofthe power transmission line channel; carrying out image target detection on the test set, updating detection model parameters, and carrying out secondary verification on the test set; and detecting the image acquired in real time by using the updated detection model, and detecting whether a large construction machinery hidden danger exists in the power transmission line channel or not. According to the construction machinery hidden danger detection method, the generalization problem of the detection model is solved, and the false alarm rate and the missing report rate are reduced.