This paper proposes a new structure of three dimensional（i. e. 3-D） filter applied to Luminance-Chrominance separation（i. e. Y-C separation as well known） in PAL TV signals.The 3-D filter consists of a 1-D horizontal filter and a 2-D vertical-temporal filter

where the 2-D filter can be decomposed into two 1-D filters along two new axis directions

which are oblained from suitable rotation transform from the old axis. It would be very useful for simplifying the design and implementation of 2-D filter. The new method behaves better in Y·C separation efficiency than the traditional ones. Moreover

it can avoid the trouble of motion-detection in the adaptive space filtering[1].