A noise estimation apparatus for calculating a noise estimation value of a frame of an image is provided. The noise estimation apparatus includes a distribution calculation unit, a variance calculation unit, a distribution curve generation module and a noise estimation unit. The distribution calculation unit generates a pixel distribution according to multiple pixel data of an ith block of the frame and multiple previous pixel data of the ith block of a previous frame. The variance calculation unit combines the pixel data and the previous pixel data to generate a variance value. The curve distribution generation module generates a curve distribution according to the variance value, and compares the pixel distribution with the curve distribution to generate a weighting value. The noise estimation unit outputs the noise estimation value according to the weighting value and the variance value corresponding to each of the blocks of the frame.