The invention discloses an outer-wall external thermal-insulation anti-crack mortar prepared from superfine sand. The outer-wall external thermal-insulation anti-crack mortar consists of the following ingredients in parts by weight: 25-35 parts of cement, 62-72 parts of superfine sand with fineness modulus of 0.5-0.6, 1.0-3.0 parts of shrinkage reducing agent, 0.2-0.4 part of polymer modifier, 0.1-0.3 part of water-retaining agent, and 0.05-0.15 part of fiber. When the outer-wall external thermal-insulation anti-crack mortar is in use, all the ingredients are mixed with water added in a certain ratio as required on site and are stirred uniformly. Proven by experiments, the outer-wall external thermal-insulation anti-crack mortar has the advantage of solving the technical problems such as serious shrinkage and poor construction performance obstructing the use of the superfine sand with fineness modulus of 0.5-0.6 in the anti-crack mortar; and the anti-crack mortar with the ratio of compressive strength reaching 1.90, the bonding strength reaching 1.0MPa and long operational time reaching 2h is prepared and the anti-crack mortar meets the technical requirements of JG158-2004 ETIRS (external thermal insulation rendering systems made of mortar with mineral binder and nsing wxpanded polystyrene granule as aggregate) on the anti-crack mortar.