You could get more than one peak for several reasons.

One could be that the sample is not pure and it is in fact that the different compounds that give rise to the different peaks. This depends on what kind of detector you have. It could be many different types of contamination (from septum, solvent, sample preparation etc).

It could be that there is something wrong with your injection valve so that splits the sample into parts somehow and give rise to multiple peaks.

It could be isomers of the same compound, even though this is usually not something you separate "by accident". But for some compounds it is possible.

There is also possible that your analyte is degrading or reacting with something else in the solvent or sample preparation step. This will also give rise to extra peaks (If you use a less specific detecor like UV).

You could get more than one peak for several reasons.

One could be that the sample is not pure and it is in fact that the different compounds that give rise to the different peaks. This depends on what kind of detector you have. It could be many different types of contamination (from septum, solvent, sample preparation etc).

It could be that there is something wrong with your injection valve so that splits the sample into parts somehow and give rise to multiple peaks.

It could be isomers of the same compound, even though this is usually not something you separate "by accident". But for some compounds it is possible.

There is also possible that your analyte is degrading or reacting with something else in the solvent or sample preparation step. This will also give rise to extra peaks (If you use a less specific detecor like UV).

Thank Mr. Marcus Ostman for your nice suggestions. I used Diode Array detector. My sample is not 100% soluble in mobile phase. So I used a mixture of solvents for preparation of HPLC sample and seem about 90% is soluble not totally soluble.

Mixture of inappropriate solvents can sometimes cause peak splittning but I have little experiance of that.

Thank Mr. Marcus Ostman again.It is difficult to mix my samples in mobile phase solvents. So, I used four types of solvents to prepare samples.

Every chemical compounds giving more than 1 peak, even solvent system peak will be there, so first u have to run your solvents and all reagents without active compound and then delete all extra peaks from spectra.

In every compound few impurities always there so check ur compounds monograph their all impurities and theirs limits will be there, so consider those impurities as granted impurities.

I agree with the answer, different retention time means that not only one compound present in a sample.. more purification may be needed to give the single compound in a sample

Some compounds (like monolignans containing free phenol moiety ) can react with acetic acid in HPLC solvant to form esters on-column giving second peak with sometimes the same patern (at least on MS detector).

Depending upon the conditions, it could be 3 distinct entities, differences in protonation, or potentially "decomposition" peaks (on-column or vial reactions)