We present a controllable three-dimensional fluorescence modulation technique for the high sensitive trap loss detection of ultracold molecules. The lowest vibrational levels (v = 0 and 1) of the pure long-range state 0(-)(g) (6S(1/2) + 6P(3/2)) of a cesium molecule are detected directly with high rotational resolution. Our technique proved to be a robust tool for effectively improving the detection sensitivity of trap loss spectroscopy.