ABSTRACT The bright pulsar PSR B0329+54 has been known for many years to have two emission modes. Sensitive observations of individual pulses revealed that the central component of the pulse profile, which is called the core component, is occasionally weakened considerably for a few periods and then recovered. This is the newly identified core-weak mode. Based on our long observations of PSR B0329+54 with the Jiamusi 66-m telescope at 2250 MHz, we report here that the profile components of individual pulses, including those for the core and the leading and trailing peaks, relatedly vary over some periods even before and after the core-weak mode, forming a regular pattern in the phase–time plot for a train of period-folded pulses. The pattern has a similar structure to the core-weak mode with a time-scale of 3 to 14 periods. It starts with an intensity brightening at the trailing phase of the core component, and then the core intensity decreases to a very low level, as if the core component is drifting out from the normal radiation window within 1 or 2 periods. Next the intensity in the trailing components is enhanced, and then the leading component appears at an advanced phase. Such a core-weak mode lasts for several periods. Finally, the core-weak mode ends up with an enhanced intensity at the leading phase for the core component, as if the core gradually comes back and finally stays at the phase of the profile centre, as it used to.