is used in one embodiment one circumferential layer comprises five drill bits which is shown in fig2 for annulus ring holes with a large od id difference two to three circumferential layers of drill bits can be used to cover the large annulus ring drilling area as shown in fig7 the front annulus ring percussion hammer assembly 101 shown in fig1 includes five air driven dth percussion hammers distributed and assembled over an annulus ring structural housing 400 the structural housing 400 has a prescribed housing od and a prescribed housing id the surfaces created by the housing od and housing id function as the flushing surfaces for exhaust air and drilling debris the space between the housing od and id accommodates the dth percussion hammers of which the number and size are determined by the required annulus ring hole od and id each dth percussion hammer is assembled longitudinally inside this housing space in parallel with the drilling axis of the drill string all dth percussion hammers are held and supported by the housing along its longitudinal direction referring to fig2 each drill bit 202 is fixed in its position by its two adjacent index blocks 201 the index blocks 201 prevent the drill bits 202 from self turning along the axis of its corresponding dth percussion hammer the index blocks 201 are specifically built to withstand the torque and thrust forces experienced by the drill bits 202 during the drilling process with the annulus ring drilling percussion hammer assembly rotating and each drill bit 202 impacting the ground the indexing of each drill bit 202 also restricts it from self turning so as to allow maximum possible ground impacting.