Quasi-continuous observations of PSR B0329+54 over 20 days using the Nanshan 25-m telescope at 1540 MHz have been used to study the effects of refractive scintillation on the pulsar flux density and diffractive scintillation properties . Dynamic spectra were obtained from datasets of 90 min duration and diffractive parameters derived from a two-dimensional auto-correlation analysis . Secondary spectra were also computed but these showed no significant evidence for arc structure . Cross correlations between variations in the derived parameters were much lower than predicted by thin screen models and in one case was of opposite sign to the prediction . Observed modulation indices were larger than predicted by thin screen models with a Kolmogorov fluctuation spectrum . Structure functions were computed for the flux density , diffractive timescale and decorrelation bandwidth . These indicated a refractive timescale of 8 \pm 2 h , much shorter than predicted by the thin screen model . The measured structure-function slope of 0.4 \pm 0.2 is also inconsistent with scattering by a single thin screen for which a slope of 2.0 is expected . All observations are consistent with scattering by an extended medium having a Kolmogorov fluctuation spectrum which is concentrated towards the pulsar . This interpretation is also consistent with recent observations of multiple diffuse scintillation arcs for this pulsar .