Abstract: At Tarapoa Block in Ecuador, the top formation is young and undercompacted with short deposition time, so wellbore instability tends to happen easily in the process of well drilling, and leads to balling up, mud making and other problems. In order to solve these problems, a calcium-base drilling fluid system with strong plugging capacity was researched based on flocculation and inhibition property of calcium ion, combined with physical plugging, and then it was evaluated indoors. It is shown that the calcium-base drilling fluid system with strong plugging capacity has primary recovery ratio of 88.28%, swelling capacity of clay core of 4.287 mm, core plugging rate over 95% and clay pollution resistance over 10% and it is characterized by flocculated cuttings, strong inhibition, high plugging capacity and strong cutting pollution resistance. It was applied to more than 10 wells in Tarapoa Block. It is indicated that the calcium-base drilling fluid system with strong plugging capacity is advantageous with remarkable anti-collapse effect, controllable density and stable rheological property. And its application solves the difficulty of drilling fluid technology in the top formation of Tarapoa Block, improves the rate of penetration, assures the smooth tripping in and out and lowers the casing to bottom hole safely. In short, the calcium-based drilling fluid with strong plugging capacity fully satisfies the needs of safe drilling in the top formation of Ecuador.