The surface morphology and interior flaws of KTiOPO4 (KTP) crystals grown in pota-sium polyphosphates flux solution were observed with optical microscopy. The fluctuation pattern of bulk supersaturations across the layer-like floss in the crysrals was obtained with scanning electron microscope and energy spectrum analysis. Based on the above results, the causes and process for the formation of macro inclusion-layer-like floss due to the high in-homogeneity of solute distribution on the grown face under some inappropriate growth conditions were elucidated. The flossless and transparent KTP crystals have been grown rapeatedly when the cocentrations of solution were located in the region of critical bulk supersaturation for steady growth, namely the σ was everywhere larger than the lower limit (～1.3) of the region.