i think some other particles are contaminating and what is your solvent ?? compare UV-Vis spectra of solvent with sample

i have used methanol and ethanol,my plant extract are in methanol and ethanol,should i dry the plant extract to powder and dissolve this water in water and than make nanoparticles for that probably i will need to use DMSO,will it work or will hinder in nanoparticle making process?

I don't really understand the procedure you mentioned, but if you are using an extract, it is likely to contain many substances, each with its own absorbance spectrum. It is therefore unsurprising that you are getting multiple peaks. I would guess that these represent mostly chlorophylls, flavonoids, carotenoids, and other plant pigments.

http://www.hindawi.com/journals/jnp/2014/967802/

i have followed the same procedure as given in this paper,i used aqueous,methanol and ethanol extracts,thanks

Each nanoparticle shows peak. In addition to this, residual precursor which is present in the solution and plant extract  contain many substances also gives absorbance spectrum. I think the multiple peaks are due to the precursor, nanoparticle and biomolecules in the plant extract.

Try taking UV-Vis spectra with your plant alcohol extract as the baseline instead of water as the baseline. This should subtract the peaks due to the biological extract.