We numerically investigate the effects of a weak coherent femtosecond (fs) pulse seed on the continuous wave (CW) pumped supercontinuum (SC) generation. We analyze the evolution of CW pumped SC generation with various random noises and we observe the instabilities, which are initiated by modulation instability, in the spectrum of the SC. To actively control the instabilities, we introduce a weak coherent fs pulse seed to improve the properties of CW pumped SC in terms of spectral bandwidth and pulse-to-pulse stability. The detailed numerical results corroborate that the frequency shift and the peak power of the seed significantly decide the properties of the SC. The present investigation would be highly useful for realizing a broad CW pumped SC with enhanced coherence and SNR. © 2018 IOP Publishing Ltd.