The invention relates to a power transformer winding looseness diagnosis method based on a load state, which belongs to the technical field of power transformer safety monitoring. The method comprises the steps that 1) sampling frequency and time are set; 2) the B-phase low voltage side current of a power transformer is measured; 3) a vibration signal of each vibration sensor is acquired; 4) a first threshold and a second threshold are calculated; 5 ) whether the first threshold and the second threshold are set is determined; 6) the power transformer in the load state is monitored, and looseness is determined; and 7) if the result of three consecutive times of determining is that a first characteristic value is greater than the first threshold and a second characteristic value is greater than the second threshold, a winding of the power transformer is loose; if the result of three consecutive times of determining is not that the first characteristic value is greater than the first threshold and the second characteristic value is greater than the second threshold, the process returns to the step 6 ). According to the method, winding looseness diagnosis is carried out through the relationship between fundamental frequency and the frequency doubling component, and the problem of poor accuracy is avoided.