According to observation to the rock samples from 6 outcrops of Lower Ordovician Majiagou Member-3 carbonate rock in the northwest of Henan province, the Majiagou Member-3 mostly consists of micritic limestone full of typical burrow fillings associated with trace fossils. Based on analysis to burrow fillings, diagenesis experienced mainly is dolomitization, cementation, dissolution, compaction-pressolution and dedolomitization during four periods of diagenesis. It is known that dissolution plays a constructive role in filling pore development and compaction and dedolomitization play a destructive role while dolomization, cementation and pressolution do dual influence. Intercrystalline pores, intercrystalline dissolution pores and intracrystal secondary dissolution pores are the main types of burrow fillings pores. The porosity of burrow fillings experienced twice evolutions from lower to higher as diagenetic environments changed. The dolomitization had done the best contribution for pore development during early diagenetic stage and subsequent increase of porosity mainly depended on leaching and dissolution of atmospheric fresh water in supergene environment. It is proved that diagenetic reformation to burrow fillings in trace fossils can finally improve the reservoir property of host rock.