The invention discloses a well cementing preflush, and relates to an enhanced coal bed cementing type preflush system. The enhanced coal bed cementing type preflush system is prepared from the following components in parts by weight: 0.65 to 3.2 parts of plugging agent, 2.3 to 12.5 parts of auxiliary filling agent, 0.82 to 2.5 parts of performance regulating agent, 0.19 to 0.85 part of surfactant, 0.3 to 0.6 part of defoaming agent and 81.5 to 95 parts of water. The enhanced coal bed cementing type preflush system has the advantages that on the basis of self properties of the coal bed layer, the improving of surface wetting property of the coal bed is considered so as to improve the surface wetting property of the coal bed; by adding the surfactant into the well cementing preflush, and controlling the ratio of certain components in the well cementing preflush, the well cementing quality preflush system of a coal bed gas well has good compatibility with drilling liquid and cement slurry, the surface wetting property of the coal is well improved, the coal core has good water wetting property, the cementing strength of a second interface of the well cementing is improved, and various performances and indexes can meet the site well cementing requirements.