Objective To observe the changes of left ventricular strain parameters in patients with colorectal cancer before and after combined chemotherapy with FOLFOX. Methods 30 healthy people were selected as normal group, and 30 patients with pathologically diagnosed colorectal cancer and FOLFOX (5-fluorouracil +oxaliplatin+calcium leucovorin) chemotherapy were collected. Before, after 1 cycle of chemotherapy, after 6 cycles of chemotherapy, and within 48 hours after 12 cycles of chemotherapy, cardiac ultrasound examination was performed, and dynamic images of the left ventricle were collected to obtain conventional parameters: LVEDd, LVEDs, IVSd, LVPWd, LVEDV, LVESV, LVEF, LVFS; three-dimensional parameters: SPI, SV, CO, LVEDMass, LVESMass, GAS, GRS, GLS, GCS, and the changes of these values before and after chemotherapy were compared. Results Compared with the chemotherapy group, the normal group had no statistically significant changes in LVEDd, LVEDs, IVSd, LVPWd, LVPW, LVESV, and SPI (P>0.05); LVEF, LVFS, SV, CO were in the middle and late stages of chemotherapy. There was a decrease, the difference was statistically significant (P<0.05), HR, LVEDMass, LVEESMass were slightly increased, the difference was statistically significant (P<0.05); LGS and GAS after chemotherapy were significantly lower than before chemotherapy (P<0.05), the area under the ROC curve of GAS is 0.883, P=0.000, 30% is selected as the diagnostic boundary, the sensitivity is 86.7%, and the specificity is 80%; the area under the ROC curve of GLS is 0.888, P=0.000, 19% as a diagnostic boundary, the sensitivity is 73.3% and the specificity is 90.0%. Conclusion Three-dimensional speckle tracking technology can detect the changes of left ventricular function in patients with colorectal cancer caused by FOLFOX in early stage, of which LVLGS and LVGAS are powerful observation indicators.