A classical joint transform correlator (JTC) usually yields large correlation sidelobes as well as a large correlation peak width, strong zero-order peak, and low diffraction efficiency, which make the detection ability of JTC lower. To overcome these difficulties, firstly, a joint power spectrum (JPS) subtraction technique in Fourier plane was proposed, where reference image power spectrum and object image power spectrum are subtracted from the JPS before inverse Fourier-transform operation, it is obvious that the modified JPS removes the zero-order term. Secondly, a fringe-adjusted filter (FAF) was presented to suppress sidelobes and noises. The modified JPS is multiplied by a FAF before the inverse Fourier-transform operation to obtain the cross-correlation peak. Computer simulations demonstrated the improved method can obviously remove zero-order diffraction and effectively suppress the sidelobes and noises compared with classic JTC, and then improve the detection ability for JTC. Experimental results presented the sharp correlation peak and also confirmed the method effectiveness.