Several fundamental problems in hydrophobic force measurements by using AFM are discussed in this paper. A novel method for colloid probe preparation based on the chemical etching technology is proposed, which is specially fit for the unique demands of the hydrophobic force measurements by AFM. The features of three different approaches for the determination of spring constants of the rectangular cantilevers, including geometric dimension, Cleveland and Sader methods are compared. The influences of the sizes of the colloids on the measurements of the hydrophobic force curves are investigated. Our experimental results showed that, by selecting a colloid probe with a proper spring constant and a tip size, a real hydrophobic force, even the complete hydrophobic interaction force curve with every subtle change in details might be measured by using AFM.