In a liquid rocket engine test，the signals transmitted by flow and rotating speed sen·
sors are irregular frequency signals．Therefore，modulations of these signals are the key links for ac—
curate measurement．In this paper the signal modulating technique of flow and rotating speed parameters
was introduced，the principals，function and the key points of design and test methods were
emphatically illustratied．The principal figure of the key link of frequency signal modulators was
presented．The described frequency signal modulators directly modulate the frequency signals transmitted
by the flow and rotating speed sensors during LOX／kerosene rocket engine tests．The accurate
measurement of frequency parameters can be reached by applying the modulators．