We propose a novel Fast dimensionreduc-ing ranked query method (FDRQM) with high security for encrypted cloud data.We use Principal component analysis (PCA) algorithm to improve the speed of data encryption and search efficiency.Moreover,a random threshold of accumulated contribution rate of principal components is set to realize the randomness of data dimension reduction and improve data security further.Besides,we introduce a unit matrix before dimension reduction of index,which can not only improve the security of the system,but also ensure the accuracy of query.We demonstrate that our algorithm is more effective and efficient than existing algorithms.