The invention belongs to the technical field of quantum machine learning, and discloses a selectable accurate quantum principal component analysis method and application, wherein based on a quantum singular value threshold decomposition algorithm, compared with traditional quantum principal component analysis, the flexibility is high, main components, namely main characteristic value characteristic vectors, are output by controlling thresholds, and all components, namely all eigenvalue eigenvectors, can be output, and compared with the previous improved algorithm, the algorithm reduces the number of quantum gates in the parallel direction, and the result is more accurate. According to the invention, the accurate quantum principal component analysis algorithm selected by the invention mainly comprises seven steps of inputting a covariance matrix quantum state, extracting a characteristic value through phase estimation, converting the characteristic value, performing controlled overturning, performing inverse transformation, measuring, extracting and screening the characteristic value through phase estimation, and finally outputting the characteristic value greater than a given threshold value and a corresponding characteristic vector; and the method can be used as a subroutine of other algorithms in the field of quantum machine learning, and the execution efficiency of the wholealgorithm is improved.