Disclosed is a deblocking filter level decision method applicable to an image encoder and used for determining deblocking filter levels of N image frames. The method includes: determining whether a current quantization parameter of a current frame of the N image frames is the same as a previous quantization parameter of any previous frame of the N image frames; if the current quantization parameter is different from the previous quantization parameter, looking up M current deblocking filter reference levels in an established table according to the current quantization parameter and then determining M current deblocking filter levels of the current frame according to the M current deblocking filter reference levels, respectively; and if the current quantization parameter is the same as the previous quantization parameter, determining the M current deblocking filter levels of the current frame according to M previous deblocking filter levels of the previous frame, respectively.