The invention provides a production technology of nitrogen-phosphorus series flame-retardant viscose filaments. The production technology comprises the following steps: A. carrying out impregnation ona pulp raw material by alkali liquor, grinding the impregnated raw material by using a grinder, squeezing, and carrying out crushing treatment to obtain alkali cellulose; B. sequentially carrying outaging treatment, sulfonating treatment, dissolving treatment, defoaming treatment and maturing treatment on the alkali cellulose; when the alkali cellulose is mature, adding nitrogen-phosphorus series flame retardant slurry into a viscose solution so as to enable the amount of a flame retardant to be 0.5-3% of the content of methyl cellulose in viscose; then, respectively adding the nitrogen-phosphorus series flame retardant slurry into viscose solutions obtained by first KKF filtering, second plate frame filtering and third plate frame filtering so as to enable the amount of the flame retardant to reach a set value, and then carrying out fourth plate frame filtering to obtain a spinning solution for spinning; C. extruding the spinning solution for spinning from a spinning nozzle of a spinning machine, solidifying by using spinning bath, and drafting by using a drafting machine to obtain tows; refining and drying the tows to obtain the flame-retardant viscose filaments. The technologyenables the flame retardant to be well dispersed in the viscose and evenly mixed with the viscose, thus avoiding the impact on the strength of fibers to the utmost extent.