I do not know this specific equipment, regardless, if you have a noticable broadening of  peak when running many types of equipment that a sample is flowing through, that suggests a particle or particles, clogging the flow through.  Since you mentioned injection, perhaps something similar.  If item is volitized, the gas release and response may be restricted.  If the peak values are reduced over time, that is another indicator.  I might also contact analytical tech support with equipment company, as it may be something else, such as a detector with weakening signal or response.

Thanks for your reply William.. I injected Diluent in between the samples on waters Alliance HPLC ,still the third injection peak was broadening.. please suggest

Equipment technical support is often free as they want you to like the equipment, and when its time, replace it with them.  You did not say if peak was as high as before when peaks were not broadened. As long as you are using standard concentrations regularly, such as before and after sample, you should be OK.  Also look over equipment instructions and maintenance information, sometimes there are maintenance or operational indicators.