NOVELTY - Preparation of N-alkyl conjugated ionic quaternary ammonium salt involves carrying out carbonylation reaction, reacting bis(trichloromethyl)carbonic ester solution (II) into toluene dialkylamine (III), adding acid-binding agent, extracting, decompressing and distilling, filtering, washing filter cake, obtaining chlorinated salt (VI), dissolving chlorinated salt in dichloromethane or chloroform, dropping tetramethylguanidine, obtaining guanidine salt mixture (VII), mixing guanidine salt mixture, adding methanol, filtering, adding toluene, crystallizing and filtering.    USE - Preparation of N-alkyl conjugated ionic quaternary ammonium salt (claimed).    ADVANTAGE - The N-alkyl conjugated ionic quaternary ammonium salt is economically prepared with high yield without polluting the environment, by a simple method.    DETAILED DESCRIPTION - Preparation of N-alkyl conjugated ionic quaternary ammonium salt involves carrying out carbonylation reaction at 5-10 degrees C, reacting bis(trichloromethyl)carbonic ester solution of formula: Cl3CO-C(=O)-OCCl3 (II) into toluene dialkylamine of formula (III), adding acid-binding agent, finishing dripping, stirring at room temperature and reacting for 4-10 hours, separating, extracting, decompressing and distilling, obtaining tetraalkyl bis(trichloromethyl)carbonic ester of formula (IV) and dialkyl amine of formula (V) in the molar ratio of 1:2-1:15, performing chlorination reaction at 5-10 degrees C, providing toluene solution of tetra-alkyl urea, adding solution of bis(trichloromethyl) carbonate in toluene, heating to room temperature, stirring reaction, adding and stirring for 2-10 hours, filtering, washing the filter cake, obtaining chlorinated salt of formula (VI), dissolving chlorinated salt in dichloromethane or chloroform, dropping tetramethylguanidine at 5-10 degrees C, warming to room temperature with stirring, adding and stirring for 2-8 hours, obtaining guanidine salt mixture of formula (VII), mixing guanidine salt mixture, adding methanol to dissolve, adding solution of sodium methoxide at room temperature for 2-8 hours, filtering, removing methanol by distillation, adding toluene, crystallizing at 0-25 degrees C and filtering. The molar ratio of acid binding agent to dialkyl amine is 1:1-2:1. The molar ratio of tetraalkyl urea and bis(trichloromethyl)carbonate is 1:1-1:5. The molar ratio of chloride salt and tetramethylguanidine is 1:2-1:5.    R1,R2=saturated, unsaturated or linear 1-16C alkyl;and    A=chloride ion.