The invention provides a roof plate system with waterproofness improved. The roof plate system comprises roof purlines and roof plates, each two adjacent roof plates are fixedly connected through a locking device which comprises a support keel and a buckle cover, the upper end of each roof plate is clamped between the corresponding support keel and the corresponding buckle cover, and each locking device is mounted on the corresponding roof purline through a conversion member; the edge of each buckle cover is provided with a flange extending toward the outer side in an obliquely downward manner, each support keel is positioned in a vertical projection of the corresponding buckle cover, a threaded hole is formed in each buckle cover, each roof plate is fixed and compressed between the corresponding support keel and the corresponding buckle cover through a bolt, a cover cap is arranged above each buckle cover, and each bolt covers in the corresponding cover cap. A fixing mode through the buckle covers is adopted, and each buckle cover covers the corresponding bolt and a joint of the corresponding roof plate and the corresponding support keel, so that no screw of a roof is exposed, the whole roof is attractive, potential trouble in water leaking caused by existing screws is eliminated completely, and waterproofness of the roof plate system is improved.