NOVELTY - A double-layer silicon nitride antireflection coating is prepared by (A) depositing washed, haired diffused and corroded crystalline silicon by test tube plasma-enhanced chemical vapor deposition (PECVD) to obtain high-refractive index silicon nitride antireflection coating; (B) closing silane flow for 1-2 minute after obtaining high-refractive index silicon nitride antireflection coating, and keeping ammonia flow and radio power unchanged; and (C) re-depositing obtained antireflection coating in test tube PECVD to obtain desired double-layer silicon nitride antireflection coating.    USE - Method for preparation of double-layer silicon nitride antireflection coating (claimed) for crystalline silicon solar battery.    ADVANTAGE - The prepared coating improves inactivation effect on surface of solar battery, reduces refractive index of battery pieces, benefits short circuit current and open voltage of batteries, thus improving conversion percentage of solar batteries.    DETAILED DESCRIPTION - Double-layer silicon nitride antireflection coating is prepared by (A) depositing washed, haired diffused and corroded crystalline silicon by test tube plasma-enhanced chemical vapor deposition (PECVD) to obtain high-refractive index silicon nitride antireflection coating; (B) closing silane flow for 1-2 minute after obtaining high-refractive index silicon nitride antireflection coating, and keeping ammonia flow and radio power unchanged; and (C) re-depositing obtained antireflection coating in test tube PECVD to obtain desired double-layer silicon nitride antireflection coating. The PECVD parameter in step (A) comprises ammonia flow of 3-5.5 standard liters per minute (slm), silane flow of 700-850 standard cubic centimeter per minute (sccm), pressure 1400-1700 mTorr, radio power of 3700-4000 w, and switch time 5:30 minutes (ms), and time of 100-200 seconds (s). The PECVD parameter in step (C) comprises ammonia flow of 4-5.5 slm, silane flow of 200-350 sccm, pressure of 1300-1500 mTorr, radio power of 3700-4000 w, switch time of 5:30 ms and time of 380-450 s.